Zeitschriftenartikel zum Thema „Bubble/foam lifetimes“

Foams play an essential role in food. They contribute to the texture, aroma, and mouthfeel of a product; potentially reduce calories; and visually inspire the consumer. Understanding factors that control foam structure and bubble lifetimes is, therefore, of considerable interest. This review focuses on the effect of the continuous phase rheology for bubbly systems with an emphasis on edible foams. We review common biopolymers used to alter the rheology of the continuous phase of food foams and discuss potential mechanisms responsible for the production and stabilization of such systems. Variations to the matrix (i.e., foamulsions and oil-based foams) and the addition of gelling particles are also considered. This review emphasizes the necessity for fine control over the mechanical properties of the continuous phase to achieve the desired sensorial attributes and foam stability in food products. However, the dynamics of viscoelastic food foams are poorly understood due to their complex nature. We, therefore, discuss rheological studies on model foams and provide future directions for research that is in keeping with current trends and challenges in the food industry and culinary arts.

We have studied the effect of cell boundary on 2D foam, with particular attention to perfect arrays of identical bubbles, and those containing only a single defect with time. We have also examined the effect of the wetness of the foam, observing the stability of two-dimensional foam comprising bubble rafts constrained to a fixed area of liquid surface. Perfectly six-fold coordinated foam appear to be unstable against loss of cohesion, but the lifetime to breakage of the perfect foam increases systematically with changing the cell boundaries. Foams containing a single defect are stable against such breakage due to the elastic stress fields around it.

The use of foams to deliver bioactive agents and drugs is increasing in pharmaceutics. One example is the use of foam as a delivery system for polidocanol (POL) in sclerotherapy, with the addition of bioactive compounds to improve the delivery system being a current subject of study. This work shows the influence of two bioactive additives on the structure and stability of POL foam: hyaluronic acid (HA) and Pluronic-F68 (F68). HA is a natural non-surface-active biopolymer present in the extracellular matrix while F68 is a surface-active poloxamer that is biocompatible with plasma-derived fluids. Both additives increase the bulk viscosity of the sample, improving foam stability. However, HA doubled and F68 quadruplicated the foam half lifetime of POL. HA reduced the size and polydispersity of the bubble size distribution and increased the surface elasticity with respect to POL. Both facts have a positive impact in terms of foam stability. F68 also altered bubble structure and increased surface elasticity, again contributing to the enhancement of foam stability. The surface characterization of these systems is important, as in foam sclerotherapy it is crucial to assure the presence of POL at the surface of the bubbles in order to deliver the sclerosant agent in the target vein.

Liquid foams are concentrated dispersions of gas bubbles in a small amount of surfactant solution, which are perpetually out of equilibrium systems. The process of liquid draining through networks of Plateau borders in a fresh foam is so-called foam drainage, as a result of both gravitational and capillary forces, which has great effect on the stability of foams. From the view of foam physics and dynamics, this paper briefly introduces foam structure and major lifetime limiting factors of foam. The substantial progress on the theory of drainage, measuring techniques for liquid fractions, drainage in both one dimension and two dimensions, and drainage in microgravity circumstances are overviewed throughout. Remaining tasks are discussed and a multiscale methodology for foam drainage is proposed for future investigations.

Abstract A laboratory experiment to quantify whitecap foam decay time in the presence or absence of surface active material is presented. The investigation was carried out in the glass seawater channel at the Hydraulics Facility of Scripps Institution of Oceanography. Whitecaps were generated with focused, breaking wave packets in filtered seawater pumped from La Jolla Shores Beach with and without the addition of the surfactant Triton X-100. Concentrations of Triton X-100 (204 μg L−1) were chosen to correspond to ocean conditions of medium productivity. Whitecap foam and subsurface bubble-plume decay times were determined from digital images for a range of wave scales and wave slopes. The experiment showed that foam lifetime is variable and controlled by subsurface bubble-plume-degassing times, which are a function of wave scale and breaking wave slope. This is true whether or not surfactants are present. However, in the presence of surfactants, whitecap foam is stabilized and persists for roughly a factor of 3 times its clean seawater value. The range of foam decay times observed in the laboratory study lie within the range of values observed in an oceanic dataset obtained off Martha’s Vineyard in 2008.

In the oil industry, oil foams can be found at different steps from the crude oil treatment to the gas stations. Their lifetime can sometimes reach several hours and be much longer than the residence times available for gas/liquid separation. However, the conditions of formation and stability of such foams have been poorly studied in the literature, in contrast to the foamability of aqueous systems. On the fields, it is currently observed that crude oils enriched with asphaltenes form particularly stable foams. In this work, we have studied the influence of asphaltenes on the foamability of oil mixtures. All the experiments were performed on model systems of crude oils, that-is-to-say decane/toluene mixtures containing asphaltenes at concentrations ranging from 0.01 to 5 wt%. We in particular demonstrate that, within the investigated concentration range, asphaltenes from two different wells do not have any significant surface active properties despite their contribution to the foamability of oil mixtures. We show that the formation of an asphaltene layer at the interface with air that has been evidenced in the past results from solvent evaporation. Using a recently developed experiment based on the Marangoni effect with our model oils, we demonstrate that asphaltenes are not surface active in those oils. We further characterize the oil foamability by measuring the lifetime of the foam formed by blowing nitrogen through the liquid in a column. At concentrations larger than 1 wt%, asphaltenes significantly enhance the foamability of the oil mixtures. Moreover, the closer the asphaltenes are to their limit of precipitation the larger the foamability. However, we evidence that the oil mixtures themselves foam and we show the importance to consider that effect on the foamability. In addition, we observe that the foamability of the asphaltenes solutions unexpectedly varies with the initial height of the liquid in the column. We suggest that, although not significantly modifying the surface tension, the asphaltenes could be trapped at the oil/gas interface and thus prevent bubble coalescence.

Summary This paper reports the study of the effect of different ions (monovalent, bivalent, and multiple ions) on nanosilica-stabilized carbon dioxide (CO2) foam generation. CO2 foam was generated by coinjecting CO2/5,000 ppm nanosilica dispersion (dispersed in different concentrations of brine) into a sandstone core under 1,500 psi and at different temperatures. A sapphire observation cell was used to determine the foam texture and foam stability. Pressure drop across the core was measured to estimate the foam mobility. The results indicated that more CO2 foam was generated as the sodium chloride (NaCl) concentration increased from 1.0 to 10%. In addition, the foam bubble became smaller and foam stability improved with the increase in NaCl concentration. The CO2-foam mobility decreased from 13.1 to 2.6 md/cp when the NaCl concentration increased from 1 to 10%. For the bivalent ions, the generated CO2-foam mobility decreased from 19.7 to 4.8 md/cp when CaCl2 concentration increased from 0.1 to 1.0%. Synthetic produced water with total dissolved solids (TDS) of 18,583 ppm was prepared to investigate the effect of multiple ions on foam generation. The results showed that stable CO2 foam was generated as the synthetic produced water and nanosilica dispersion/CO2 flowed through a porous medium. The lifetime of the foam was observed to be more than 2 days as the foam stood at room temperature. Mobility of the foam was calculated as 5.2 md/cp.

Among the various interventions proposed to remediate the health and security effects of climate change by solar radiation protection is the proposal to enhance natural ocean whitecap formation. Compared to other solar protection interventions, this is technically simple and quickly terminated. However, it has a drawback: even if the energy be obtained from wind or wave, the power demand to maintain a foam raft determines the capitalization of equipment. The average power demand is inversely related to foam lifetime which can be prolonged by surfactants preferably derived from ingenerate resources. Here, we estimate the associated energy and power demands by identifying the parameters that can be adjusted to moderate the capital cost of implementation. Before dividing by efficiency factors, the range of power demand for an intermediate areal energy requirement of 5 MJ/km2 of ocean varies from 6 to 30 W/km2 for foam lifetime of 10–2 days. The most likely route to deployment is through merchant ship lubrication using bubbly liquids which both reduces fuel consumption and creates an extended wake and is perhaps an example of technical symbiosis.

Foam-related parameters are associated with beer quality and dependent, among others, on the protein content. This study aimed to develop a machine learning (ML) model to predict the pattern and presence of 54 proteins. Triplicates of 24 beer samples were analyzed through proteomics. Furthermore, samples were analyzed using the RoboBEER to evaluate 15 physical parameters (color, foam, and bubbles), and a portable near-infrared (NIR) device. Proteins were grouped according to their molecular weight (MW), and a matrix was developed to assess only the significant correlations (p < 0.05) with the physical parameters. Two ML models were developed using the NIR (Model 1), and RoboBEER (Model 2) data as inputs to predict the relative quantification of 54 proteins. Proteins in the 0–20 kDa group were negatively correlated with the maximum volume of foam (MaxVol; r = −0.57) and total lifetime of foam (TLTF; r = −0.58), while those within 20–40 kDa had a positive correlation with MaxVol (r = 0.47) and TLTF (r = 0.47). Model 1 was not as accurate (testing r = 0.68; overall r = 0.89) as Model 2 (testing r = 0.90; overall r = 0.93), which may serve as a reliable and affordable method to incorporate the relative quantification of important proteins to explain beer quality.

Whitecap foam generated by wind-driven wave breaking is distinguished as either active (stage A) or residual (stage B). Discrimination of whitecap stages is essential to quantify the influence of whitecaps on the physical and chemical processes at the marine boundary layer. This study provides a novel method to identify whitecap stages based on visible imagery using particle image velocimetry (PIV). Data used are from a Gulf of Mexico cruise where collocated infrared (IR) and visible cameras simultaneously recorded whitecaps. IR images were processed by an established thresholding method to determine stage A lifetime from brightness temperature. The visible images were also filtered using a thresholding method and then processed using PIV to estimate the average whitecap velocity. A linear relationship was established between the lifetime of stage A and the timescale of averaged velocity. This novel method allows stage A whitecap lifetime to be determined using whitecap velocity and provides an objective approach to separate whitecap stages. This method paves the way for future research to easily quantify whitecap stages using affordable off-the-shelf video cameras. Results, which include evidence that whitecaps stop advancing before stage A ends and may be an indication of bubble plume degassing, are discussed.

AbstractActive and total whitecap fractions quantify the spatial extent of oceanic whitecaps in different lifetime stages. Total whitecap fraction W includes both the dynamic foam patches of the initial breaking and the static foam patches during whitecap decay. Dynamic air–sea processes in the upper ocean are best parameterized in terms of active whitecap fraction WA associated with actively breaking crests. The conventional intensity threshold approach used to extract WA from photographs is subjective, which contributes to the wide spread of WA data. A novel approach of obtaining WA from energy dissipation rate ε is proposed. An expression for WA is derived in terms of energy dissipation rate WA(ε) on the basis of the Phillips concept of breaking crest length distribution. This approach allows more objective determination of WA using the breaker kinematic and dynamic properties yet avoids the use of measuring breaking crest distribution from photographs. The feasibility of using WA(ε) is demonstrated with one possible implementation using buoy data and a parametric model for the energy dissipation rate. Results from WA(ε) are compared to WA from photographic data. Sensitivity analysis quantifies variations in WA estimates caused by different parameter choices in the WA(ε) expression. The breaking strength parameter b has the greatest influence on the WA(ε) estimates, followed by the breaker minimal speed and bubble persistence time. The merits and caveats of the novel approach, possible improvements, and implications for using the WA(ε) expression to extract WA from satellite-based radiometric measurements of W are discussed.

AbstractFoams are unstable jammed materials. They evolve over timescales comparable to their “time of use", which makes the study of their destabilisation mechanisms crucial for applications. In practice, many foams are made from viscoelastic fluids, which are observed to prolong their lifetimes. Despite their importance, we lack understanding of the coarsening mechanism in such systems. We probe the effect of continuous phase viscoelasticity on foam coarsening with foamed emulsions. We show that bubble size evolution is strongly slowed down and foam structure hugely impacted. The main mechanisms responsible are the absence of continuous phase redistribution and a non-trivial link between foam structure and mechanical properties. These combine to give spatially heterogeneous coarsening. Beyond their importance in the design of foamy materials, the results give a macroscopic vision of phase separation in a viscoelastic medium.

AbstractLiquid foams respond plastically to external perturbations over some critical magnitude. This rearrangement process is directly related to the mechanical properties of the foams, playing a significant role in determining foam lifetime, deformability, elasticity, and fluidity. In this paper, we experimentally investigate the rearrangement dynamics of foams near a dry-wet transition. When a foam transforms from a dry state to a wet state, it is found that considering collective events, separated T1 events propagate in dry foams, while T1 events occur simultaneously in wet foams. This cross over to collective rearrangements is closely related to the change in local bubble arrangements and mobility. Furthermore, it is also found that a probability of collective rearrangement events occurring follows a Poisson distribution, suggesting that there is little correlation between discrete collective rearrangement events. These results constitute progress in understanding the dynamical properties of soft jammed systems, relevant for biological and material sciences as well as food science.

AbstractGravity‐induced drainage is one of the main destabilizing mechanisms for soap bubbles and foams. Here we show that solely through acoustic levitation without introducing any chemical stabilizers, liquid drainage in the bubble film can be completely inhibited, therefore leading to a significant enhancement of bubble lifetime by more than two orders of magnitude and enabling the bubble to survive puncturing by a needle. Based on sound simulation and force analysis, it has been found that acoustic radiation force, exerted on both the inner and outer surfaces of the levitated bubble, acts in opposite directions, thus providing a squeezing effect to the bubble film. The hydrostatic pressure that induces drainage has been balanced by the acoustic radiation pressure exerted on both sides of the film, which is at the origin of the sound stabilization mechanism. This study provides new insights into the interplay between sound and soap bubbles or films, thus stimulating a wide range of fundamental research concerning bubble films and expanding their applications in bio/chemical reactors.

Aims / Objectives: To find the lifetime of the bubble by plotting the rate of mass flow rate change against time. Place and Duration of Study: Department of Mathematics and Applied Science, Catholic University of Eastern Africa, Nairobi, Kenya, between February 2020 and March 2021. Methodology: The maximum lifetime of the bubble is assumed to match the time when the mass flow rate change is zero. The study also assumes the velocity of flow rate and other fluid properties at the interface of fuel-surfactant constant other than Re. Re is varied from 0.01 to 100. Results: The graphical plots show that for Re ! 1, and Re " 1, the stability depends on diffusive viscosity and linearized convection, respectively. The simulation suggested that the bubble formed at the fuel-surfactant interface may have Re “ 1 and its lifetime is tb » 0.28. Conclusion: The lifetime of surfactant depends on Re while assuming other interface properties constant. Recommendation: Future studies in the area need to consider the effect of variation in temperature, velocity, and Reynolds number in determining the lifetime of a bubble in the thin foam of the surfactant-fuel interface.

Foams and bubbles formed in liquid mixtures have lifetimes longer by several orders of magnitude than in pure liquids of similar viscosities. We have shown recently that this effect results from slight differences in molecular concentrations between bulk and surfaces, which give rise to a thickness-dependent surface tension of liquid films. We present a quantitative description of the enhanced stability of liquid films in binary mixtures, based on experimental data and theoretical analysis. Experiments were performed with mixtures of different natures and compositions: foams of stationary heights were obtained by continuous injection of gas, on one hand, and single bubbles were swollen under the surface of a liquid bath, on the other hand. Remarkably, the lifetimes measured in both experiments exhibit the same variations with mixture composition, and follow a power law with the microscopic length that characterises the amplitude of the thickness-dependent surface tension. In addition, the lifetimes vary with the squared film thicknesses at the onset of bursting. We suggest that two stages occur between the birth of liquid films and their rupture. We show how the thickness-dependent surface tension allows an equilibrium shape to be reached at the end of a first stretching stage. We give an analytical description of this shape, which is fully consistent with experimental findings. We suggest a possible mechanism for final rupture of the film, and discuss it in light of existing theoretical predictions. Finally, we compare the properties of liquid mixtures and surfactant solutions, and in particular their surface rheology.

In our previous study, a series of experiments had been conducted by applying different pressure depletion rates in a 1 m long sand-pack. In this study, numerical simulation models are built to simulate the lab tests, for both gas/oil production data and pressure distribution along the sand-pack in heavy oil/methane system. Two different simulation models are used: (1) equilibrium black oil model with two sets of gas/oil relative permeability curves; (2) a four-component nonequilibrium kinetic model. Good matching results on production data are obtained by applying black oil model. However, this black oil model cannot be used to match pressure distribution along the sand-pack. This result suggests the description of foamy oil behavior by applying equilibrium black oil model is incomplete. For better characterization, a four-component nonequilibrium kinetic model is developed aiming to match production data and pressure distribution simultaneously. Two reactions are applied in the simulation to capture gas bubbles status. Good matching results for production data and pressure distribution are simultaneously obtained by considering low gas relative permeability and kinetic reactions. Simulation studies indicate that higher pressure drop rate would cause stronger foamy oil flow, but the exceed pressure drop rate could shorten lifetime of foamy oil flow. This work is the first study to match production data and pressure distribution and provides a methodology to characterize foamy oil flow behavior in porous media for a heavy oil/methane system.

Introduction In 2017, 250 Indigenous delegates from across the country convened at the National Constitution Convention at Uluru to discuss a strategy towards the implementation of constitutional reform and recognition of Aboriginal and Torres Strait Islander peoples (Referendum Council). Informed by community consultations arising out of 12 regional dialogues conducted by the government appointed Referendum Council, the resulting Uluru Statement from the Heart was unlike any constitutional reform previously proposed (Appleby & Synot). Within the Statement, the delegation outlined that to build a more equitable and reconciled nation, an enshrined Voice to Parliament was needed. Such a voice would embed Indigenous participation in parliamentary dialogues and debates while facilitating further discussion pertaining to truth telling and negotiating a Treaty between Indigenous and non-Indigenous peoples. The reforms proposed are based on the collective input of Indigenous communities that were expressed in good faith during the consultation process. Arising out of a government appointed and funded initiative that directly sought Indigenous perspectives on constitutional reform, the trust and good faith invested by Indigenous people was quickly shut down when the Prime Minster, Malcolm Turnbull, rejected the reforms without parliamentary debate or taking them to the people via a referendum (Wahlquist Indigenous Voice Proposal; Appleby and McKinnon). In this article, we argue that through its dismissal the government treated the Uluru Statement from the Heart as a passing phase or mere “thought bubble” that was envisioned to disappear as quickly as it emerged. The Uluru Statement is a gift to the nation. One that genuinely offers new ways of envisioning and enacting reconciliation through equitable relationships between Indigenous and non-Indigenous populations. Indigenous voices lie at the heart of reconciliation but require constitutional enshrinement to ensure that Indigenous peoples and cultures are represented across all levels of government. Filter Bubbles of Distortion Constitutional change is often spoken of by politicians, its critics, and within the media as something unachievable. For example, in 2017, before even reading the accompanying report, MP Barnaby Joyce (in Fergus) publicly denounced the Uluru Statement as “unwinnable” and not “saleable”. He stated that “if you overreach in politics and ask for something that will not be supported by the Australian people such as another chamber in politics or something that sort of sits above or beside the Senate, that idea just won't fly”. Criticisms such as these are laced with paternalistic rhetoric that suggests its potential defeat at a referendum would be counterproductive and “self-defeating”, meaning that the proposed changes should be rejected for a more digestible version, ultimately saving the movement from itself. While efforts to communicate the necessity of the proposed reforms continues, presumptions that it does not have public support is simply unfounded. The Centre for Governance and Public Policy shows that 71 per cent of the public support constitutional recognition of Indigenous Australians. Furthermore, an online survey conducted by Cox Inall Ridgeway found that the majority of those surveyed supported constitutional reform to curb racism; remove section 25 and references to race; establish an Indigenous Voice to Parliament; and formally recognise Indigenous peoples through a statement of acknowledgment (Referendum Council). In fact, public support for constitutional reform is growing, with Reconciliation Australia’s reconciliation barometer survey showing an increase from 77 per cent in 2018 to 88 per cent in 2020 (Reconciliation Australia). Media – whether news, social, databases, or search engines – undoubtedly shape the lens through which people come to encounter and understand the world. The information a person receives can be the result of what Eli Pariser has described as “filter bubbles”, in which digital algorithms determine what perspectives, outlooks, and sources of information are considered important, and those that are readily accessible. Misinformation towards constitutional reform, such as that commonly circulated within mainstream and social media and propelled by high profile voices, further creates what neuroscientist Don Vaughn calls “reinforcement bubbles” (Rose Gould). This propagates particular views and stunts informed debate. Despite public support, the reforms proposed in the Uluru Statement continue to be distorted within public and political discourses, with the media used as a means to spread misinformation that equates an Indigenous Voice to Parliament to the establishment of a new “third chamber” (Wahlquist ‘Barnaby’; Karp). In a 2018 interview, PM Scott Morrison suggested that advocates and commentators in favour of constitutional reform were engaging in spin by claiming that a Voice did not function as a third chamber (Prime Minister of Australia). Morrison claimed, “people can dress it up any way they like but I think two chambers is enough”. After a decade of consultative work, eight government reports and inquiries, and countless publications and commentaries, the Uluru Statement continues to be played down as if it were a mere thought bubble, a convoluted work in progress that is in need of refinement. In the same interview, Morrison went on to say that the proposal as it stands now is “unworkable”. Throughout the ongoing movement towards constitutional reform, extensive effort has been invested into ensuring that the reforms proposed are achievable and practical. The Uluru Statement from the Heart represents the culmination of decades of work and proposes clear, concise, and relatively minimal constitutional changes that would translate to potentially significant outcomes for Indigenous Australians (Fredericks & Bradfield). International examples demonstrate how such reforms can translate into parliamentary and governing structures. The Treaty of Waitangi (Palmer) for example seeks to inform Māori and Pākehā (non-Maori) relationships in New Zealand/Aotearoa, whilst designated “Māori Seats” ensure Indigenous representation in parliament (Webster & Cheyne). More recently, 17 of 155 seats were reserved for Indigenous delegates as Chile re-writes its own constitution (Bartlett; Reuters). Indigenous communities and its leaders are more than aware of the necessity of working within the realms of possibility and the need to exhibit caution when presenting such reforms to the public. An expert panel on constitutional reform (Dodson 73), before the conception of the Uluru Statement, acknowledged this, stating “any proposal relating to constitutional recognition of the sovereign status of Aboriginal and Torres Strait Islander peoples would be highly contested by many Australians, and likely to jeopardise broad public support for the Panel’s recommendations”. As outlined in the Joint Select Committee’s final report on Constitutional Recognition relating to Aboriginal and Torres Strait Islander peoples (Referendum Council), the Voice to parliament would have no veto powers over parliamentary votes or decisions. It operates as a non-binding advisory body that remains external to parliamentary processes. Peak organisations such as the Law Council of Australia (Dolar) reiterate the fact that the proposed reforms are for a voice to Parliament rather than a voice in Parliament. Although not binding, the Voice should not be dismissed as symbolic or something that may be easily circumvented. Its effectiveness lies in its ability to place parliament in a position where they are forced to confront and address Indigenous questions, concerns, opinions, and suggestions within debates before decisions are made. Bursting the ‘Self-Referential Bubble’ Indigenous affairs continue to be one of the few areas where a rhetoric of bipartisan agreement is continuously referenced by both major parties. Disagreement, debate, and conflict is often avoided as governments seek to portray an image of unity, and in doing so, circumvent accusations of turning Indigenous peoples into the subjects of political point scoring. Within parliamentary debates, there is an understandable reservation and discomfort associated with discussions about what is often seen as an Indigenous “other” (Moreton-Robinson) and the policies that a predominantly white government enact over their lives. Yet, it is through rigorous, open, and informed debate that policies may be developed, challenged, and reformed. Although bipartisanship can portray an image of a united front in addressing a so-called “Indigenous problem”, it also stunts the conception of effective and culturally responsive policy. In other words, it often overlooks Indigenous voices. Whilst education and cultural competency plays a significant role within the reconciliation process, the most pressing obstacle is not necessarily non-Indigenous people’s inability to fully comprehend Indigenous lives and socio-cultural understandings. Even within an ideal world where non-Indigenous peoples attain a thorough understanding of Indigenous cultures, they will never truly comprehend what it means to be Indigenous (Fanon; de Sousa Santos). For non-Indigenous peoples, accepting one’s own limitations in fully comprehending Indigenous ontologies – and avoiding filling such gaps with one’s own interpretations and preconceptions – is a necessary component of decolonisation and the movement towards reconciliation (Grosfoguel; Mignolo). As parliament continues to be dominated by non-Indigenous representatives, structural changes are necessary to ensure that Indigenous voices are adequality represented. The structural reforms not only empower Indigenous voices through their inclusion within the parliamentary process but alleviates some of the pressures that arise out of non-Indigenous people having to make decisions in attempts to solve so-called Indigenous “problems”. Government response to constitutional reform, however, is ridden with symbolic piecemeal offerings that equate recognition to a form of acknowledgment without the structural changes necessary to protect and enshrine Indigenous Voices and parliamentary participation. Davis and her colleagues (Davis et al. “The Uluru Statement”) note how the Referendum Council’s recommendations were rejected by the then minister of Indigenous affairs Nigel Scullion on account that it privileged Aboriginal and Torres Strait Islander voices. They note that, until the Referendum Council's report, the nation had no real assessment of what communities wanted. Yet by all accounts, the government had spent too much time talking to elites who have regular access to them and purport to speak on the mob's behalf. If he [Scullion] got the sense constitutional symbolism and minimalism was going to fly, then it says a lot about the self-referential bubble in which the Canberra elites live. The Uluru Statement from the Heart stands as testament to Indigenous people’s refusal to be the passive recipients of the decisions of the non-Indigenous political elite. As suggested, “symbolism and minimalism was not going to fly”. Ken Wyatt, Scullion’s replacement, reiterated the importance of co-design, the limitations of government bureaucracy, and the necessity of moving beyond the “Canberra bubble”. Wyatt stated that the Voice is saying clearly that government and the bureaucracy does not know best. It can not be a Canberra-designed approach in the bubble of Canberra. We have to co-design with Aboriginal communities in the same way that we do with state and territory governments and the corporate sector. The Voice would be the mechanism through which Aboriginal and Torres Strait Islander interests and perspectives may be strategically placed within parliamentary dialogues. Despite accusations of it operating as a “third chamber”, Indigenous representatives have no interest in functioning in a similar manner to a political party. The language associated with our current parliamentary system demonstrates the constrictive nature of political debate. Ministers are expected to “toe the party line”, “crossing the floor” is presented as an act of defiance, and members must be granted permission to enter a “conscience vote”. An Indigenous Voice to Parliament would be an advisory body that works alongside, but remains external to political ideologies. Their priority is to seek and implement the best outcome for their communities. Negotiations would be fluid, with no floor to cross, whilst a conscience vote would be reflected in every perspective gifted to the parliament. In the 2020 Australia and the World Annual Lecture, Pat Turner described the Voice’s co-design process as convoluted and a continuing example of the government’s neglect to hear and respond to Indigenous peoples’ interests. In the address, Turner points to the Coalition of the Peaks as an exemplar of how co-design negotiations may be facilitated by and through organisations entirely formed and run by Indigenous peoples. The Coalition of the Peaks comprises of fifty Aboriginal and Torres Strait Islander community-controlled peak organisations and was established to address concerns relating to closing the gap targets. As Indigenous peak organisations are accountable to their membership and reliant on government funding, some have questioned whether they are appropriate representative bodies; cautioning that they could potentially compromise the Voice as a community-centric body free from political interference. While there is some debate over which Indigenous representatives should facilitate the co-design of a treaty and Makarrata (truth-telling), there remains a unanimous call for a constitutionally enshrined Voice to Parliament that may lead negotiations and secure its place within decision-making processes. Makarrata, Garma, and the Bubbling of New Possibilities An Indigenous Voice to Parliament can be seen as the bubbling spring that provides the source for greater growth and further reform. The Uluru Statement from the Heart calls for a three-staged approach comprising of establishing an Indigenous Voice, followed by Treaty, and then Truth-Telling. This sequence has been criticised by some who prioritise Truth and Treaty as the foundation for reform and reconciliation. Their argument is based on the notion that Indigenous Sovereignty must first be acknowledged in Parliament through an agreement-making process and signing of a Treaty. While the Uluru Statement has never lost sight of treaty, the agreement-making process must begin with the acknowledgment of Indigenous people’s inherent right to participate in the conversation. This very basic and foundational right is yet to be acknowledged within Australia’s constitution. The Uluru Statement sets the Voice as its first priority as the Voice establishes the structural foundation on which the conversation pertaining to treaty may take place. It is through the Voice that a Makarrata Commission can be formed and Indigenous and non-Indigenous peoples may “come together after a struggle” – the translation of the word’s Yolngu origins (Gaykamangu; Pearson). Only then may we engage in truth telling and forge new paths towards agreement-making and treaty. This however raises the question as to how a Voice to Parliament may look and what outcomes it aims to achieve. As discussed in the previous section, it is a question that is often distorted by disinformation and conjecture within public, political, and news-media discourses. In order to unpack what a Voice to Parliament may entail, we turn to another Yolngu word, Garma. Garma refers to an epistemic and ontological positioning in which knowledge is attained from a point where differences converge and new insights arise. For Yolngu people, Garma is the place where salt and fresh water intersect within the sea. Fresh and Salt water are the embodiments of two Yolngu clans, the Dhuwa and Yirritja, with Garma referring to the point where the knowledge and laws of each clan come into contact, seeking harmonious balance. When the ebb and flow of the tides are in balance, it causes the water to foam and bubble taking on new form and representing innovative ideas and possibilities. Yolngu embrace this phenomenon as an epistemology that teaches responsibility and obligations towards the care of Country. It acknowledges the autonomy of others and finds a space where all may mutually benefit. When the properties of either water type, or the knowledge belonging a single clan dominates, ecological, social, political, and cosmological balance is overthrown. Raymattja Marika-Munungguritj (5) describes Garma as a dynamic interaction of knowledge traditions. Fresh water from the land, bubbling up in fresh water springs to make waterholes, and salt water from the sea are interacting with each other with the energy of the tide and the energy of the bubbling spring. When the tide is high the water rises to its full. When the tide goes out the water reduces its capacity. In the same way Milngurr ebbs and flows. In this way the Dhuwa and Yirritja sides of Yolngu life work together. And in this way Balanda and Yolngu traditions can work together. There must be balance, if not either one will be stronger and will harm the other. The Ganma Theory is Yirritja, the Milngurr Theory is Dhuwa. Like the current push for constitutional change and its rejection of symbolic reforms, Indigenous peoples have demanded real-action and “not just talk” (Synott “The Uluru statement”). In doing so, they implored that Aboriginal and Torres Strait Islander peoples be involved in all decision-making processes, for they are most knowledgeable of their community’s needs and the most effective methods of service delivery and policy. Indigenous peoples have repeatedly expressed this mandate, which is also legislated under international law through the UN Declaration on the Rights of Indigenous Peoples. Coming together after a struggle does not mean that conflict and disagreement between and amongst Indigenous and non-Indigenous communities will cease. In fact, in alignment with political theories such as agonism and pluralism, coming together within a democratic system necessitates a constructive and responsive embrace of different, competing, and in some cases incommensurable views. A Voice to Parliament will operate in a manner where Indigenous perspectives and truths, as well as disagreements, may be included within negotiations and debates (Larkin & Galloway). Governments and non-Indigenous representatives will no longer speak for or on behalf of Indigenous peoples, for an Indigenous body will enact its own autonomous voice. Indigenous input therefore will not be reduced to reactionary responses and calls for reforms after the damage of mismanagement and policy failure has been caused. Indigenous voices will be permanently documented within parliamentary records and governments forced to respond to the agendas that Indigenous peoples set. Collectively, this amounts to greater participation within the democratic process and facilitates a space where “salt water” and the “bubbling springs” of fresh water may meet, mitigating the risk of harm, and bringing forth new possibilities. Conclusion When salt and fresh water combine during Garma, it begins to take on new form, eventually materialising as foam. Appearing as a singular solid object from afar, foam is but a cluster of interlocking bubbles that gain increased stability and equilibrium through sticking together. When a bubble stands alone, or a person remains within a figurative bubble that is isolated from its surroundings and other ways of knowing, doing, and being, its vulnerabilities and insecurities are exposed. Similarly, when one bubble bursts the collective cluster becomes weaker and unstable. The Uluru Statement from the Heart is a vision conceived and presented by Indigenous peoples in good faith. It offers a path forward for not only Indigenous peoples and their future generations but the entire nation (Synott “Constitutional Reform”). It is a gift and an invitation “to walk with us in a movement of the Australian people for a better future”. Through calling for the establishment of an Indigenous Voice to Parliament, a Makarrata Commission, and seeking Truth, Indigenous advocates for constitutional reform are looking to secure their own foothold and self-determination. The Uluru Statement from the Heart is more than a “thought bubble”, for it is the culmination of Indigenous people’s diverse lived experiences, outlooks, perspectives, and priorities. When the delegates met at Uluru in 2017, the thoughts, experiences, memories, and hopes of Indigenous peoples converged in a manner that created a unified front and collectively called for Voice, Treaty, and Truth. 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