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Phase behavior of concentrated microgel suspensions

English title Phase behavior of concentrated microgel suspensions
Applicant Gasser Urs
Number 132128
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Condensed Matter Physics
Start/End 01.08.2011 - 31.07.2014
Approved amount 182'652.00
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All Disciplines (2)

Discipline
Condensed Matter Physics
Physical Chemistry

Keywords (9)

colloids; microgels; soft particles; phase behavior; glass transition; crystallization; scattering; microscopy; rheology

Lay Summary (English)

Lead
Lay summary

Microgels are polymer particles with sizes in the range from 100 up to 1000nm that are immersed in a aqueous solvent. They respond reversibly to changes in their environment by changing their size. E.g. a temperature change form 20 to 40 degrees Celsius brings them from a swollen to a de-swollen state. Due to their responsiveness, microgels have great potential for applications, including drug delivery. In the swollen state the particles are soft, as they can be easily deformed. By contrast, in the de-swollen state, the particles behave very much like hard spheres. As a result, microgels are ideal systems to address the transition from hard to soft sphere behavior in one and the same system, and to study the behavior of soft particles, which has many unexplored and unknown aspects mainly due to the combination of colloid- and polymer-like behaviors that arise in these systems.

We explore the particle properties and their collective behavior when they are highly concentrated in water. Microgels offer the interesting possibility to reach very high particle concentrations that are much higher than those that can be reached with hard spheres, as microgels deform easily, can interpenetrate and shrink, and therefore can fill space much more efficiently. So far, fundamental properties like their phase behavior are not well known in this range of concentrations. The transition from the liquid to the crystal and the occurrence of an arrested state, a glass, are not well understood. Theoretical work suggests that crystal structures different from those of hard spheres should be expected for particles that are not too soft, while very soft particles are predicted not to crystallize and to stay in the liquid state. Furthermore, it has been shown that a large microgel particle in a crystal of small ones can shrink spontaneously to fit into the crystal to prevent the creation of a defect -- a behavior that cannot occur in hard-sphere systems.

The behavior of microgel particles in a glassy state at high concentrations is also far from understood, despite it has been studied to some extent with certain types of particles. With molecular substances that form glasses a wide range of behaviors has been observed as the glassy state is approached. Interestingly, recent experimental results have shown that such a wide range of behaviors is also found in microgel suspensions approaching the glassy state. However, the reasons for why this is the case are still unclear and largely unexplored.

This research project is carried out in close collaboration of the Laboratory for Neutron Scattering at Paul Scherrer Institut, Switzerland, and the Soft Condensed Matter Laboratory at the Georgia Institute of Technology, Atlanta USA. The experience and know-how of the two laboratories with complemental facilities are combined to strengthen and expand the ongoing collaboration on the properties of microgels at high concentrations. The many unexplored aspects mentioned above will be tackled using a wide range of techniques such as direct measurements of osmotic pressure, various scattering techniques, and real space imaging, which are all available. Furthermore, the PhD student working on the project profits from the international collaboration and the access to various experimental techniques.


Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Form factor of pNIPAM microgels in overpacked states
Gasser Urs, Hyatt J. S., Lietor-Santos Juan-Jose, Herman E. S., Lyon L. A., Fernandez-Nieves Alberto (2014), Form factor of pNIPAM microgels in overpacked states, in The Journal of Chemical Physics, 141, 034901.
Transient formation of bcc crystals in suspensions of poly(N-isopropylacrylamide)-based microgels
Gasser Urs, Lietor-Santos Juan-Jose, Scotti Andrea, Bunk Oliver, Menzel Andreas, Fernandez-Nieves Alberto (2013), Transient formation of bcc crystals in suspensions of poly(N-isopropylacrylamide)-based microgels, in Physical Review E, 88(12), 052308.
Crystals of microgel particles
Lietor-Santos Juan-Jose, Gasser Urs, Zhou J., Hu Z., Fernandez-Nieves Alberto (2012), Crystals of microgel particles, in Lyon L. A. (ed.), Wiley-VCHWILEY-VCH Verlag GmbH and Co. KGaA, Weinheim, Germany, 337-368.
The effect of hydrostatic pressure over the swelling of microgel particles
Lietor-Santos JJ, Sierra-Martin B, Gasser U, Fernandez-Nieves A (2011), The effect of hydrostatic pressure over the swelling of microgel particles, in SOFT MATTER, 7(14), 6370-6374.

Collaboration

Group / person Country
Types of collaboration
Georgia Institute of Technology United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
9th Liquid Matter Conference Poster Effect of polydispersity on the phase behavior of soft microgel suspensions 21.07.2014 Lisbon, Portugal Scotti Andrea;
14th Swiss Soft Day Talk given at a conference Effect of size polydispersity on the phase behavior of soft microgel suspensions 06.06.2014 Basel, Switzerland Scotti Andrea;
March Meeting of the American Physical Society 2014 Talk given at a conference Transient formation of bcc crystal in suspensions of pNIPAM-based microgels 03.03.2014 Denver, United States of America Scotti Andrea; Gasser Urs;
March Meeting of the American Physical Society 2014 Talk given at a conference Phase behavior of soft-particle suspensions as a function of size polydispersity 03.03.2014 Denver, United States of America Scotti Andrea; Gasser Urs;
12th Swiss Soft Day Talk given at a conference Transient formation of bcc crystal in suspensions of pNIPAM-based microgels 14.10.2013 Bern, Switzerland Scotti Andrea; Gasser Urs;
12th Swiss Soft Day Talk given at a conference Effect of polydispersity on the phase behavior of soft microgel suspensions 14.10.2013 Bern, Switzerland Scotti Andrea;
Joint Users' Meeting at PSI: JUM@P 2013 Poster Transient formation of bcc crystals in suspensions of pNIPAM-based microgels 18.09.2013 Villigen PSI, Switzerland Gasser Urs; Scotti Andrea;
Joint Users' Meeting at PSI: JUM@P 2013 Poster Form factor of pNIPAM microgels in over-packed states 18.09.2013 Villigen PSI, Switzerland Gasser Urs;
International Soft Matter Conference 2013 Poster Effect of polydispersity on the phase behavior of soft microgel suspensions 15.09.2013 Rome, Italy Scotti Andrea;
ICNS2013, International Conference on Neutron Scattering Poster Form factor of pNIPAM microgels in over-packed states 08.07.2013 Edinburgh, Great Britain and Northern Ireland Scotti Andrea; Gasser Urs;
ICNS2013, International Conference on Neutron Scattering Poster Effect of polydispersity on the phase behavior of soft microgel suspensions 08.07.2013 Edinburgh, Great Britain and Northern Ireland Scotti Andrea;
11th Swiss Soft Day Talk given at a conference Effect of size polydispersity on the phase behavior of soft microgel suspensions 04.06.2013 Fribourg, Switzerland Scotti Andrea;
Invited seminar on Soft Matter Science Individual talk Form factor of pNIPAM microgels in over-packed states 04.03.2013 Oxford, Great Britain and Northern Ireland Gasser Urs;
Invited seminar on microgels Individual talk Structural properties and phase behavior of densely packed microgel particles 24.09.2012 Napoli, Italy Gasser Urs;
6th Southeast Meeting on Soft Materials Interfaces Talk given at a conference Phase behavior of soft particles in presence of polydispersity 25.05.2012 Atlanta GA, United States of America Scotti Andrea;
March Meeting of the American Physical Society 2012 Talk given at a conference Effect of polydispersity on the phase behavior of soft microgel suspensions 27.02.2012 Boston MA, United States of America Scotti Andrea;
Joint Users' Meeting at PSI: JUM@P 2011 Talk given at a conference Structural properties and phase behavior of densely packed microgel particles 15.09.2011 Villigen PSI, Switzerland Gasser Urs;
8th Liquid Matter Conference Talk given at a conference Structural properties and phase behavior of densely packed microgel particles 06.09.2011 Vienna, Austria Gasser Urs;


Associated projects

Number Title Start Funding scheme
153050 Heterogenous nucleation and crystal growth of colloidal model-systems on curved surfaces 01.08.2014 Project funding (Div. I-III)
138202 Phasenverhalten von Mischungen von magnetischen und nicht-magnetischen Kolloiden 01.12.2011 Project funding (Div. I-III)
184839 Effect of particle softness and particle charge on crystallization and glass formation in colloidal microgels 01.03.2020 Project funding (Div. I-III)
113756 Phasenverhalten von Mischungen von Ferrofluiden und nicht- magnetischen Kolloiden 01.08.2007 Project funding (Div. I-III)
153050 Heterogenous nucleation and crystal growth of colloidal model-systems on curved surfaces 01.08.2014 Project funding (Div. I-III)

Abstract

Microgels are cross-linked polymer particles of colloidal sizeimmersed in a solvent. They respond reversibly to changes in theirenvironment by changing their size. Due to their responsiveness,microgels have great potential for applications, including drugdelivery. In the swollen state the particles are soft, as they canbe easily deformed. By contrast, in the de-swollen state, theparticles behave very much like hard spheres. As a result, microgelsare ideal systems to address the transition from hard to soft spherebehavior in one and the same system, and to study the behavior ofsoft particles, which has many unexplored and unknown aspects mainlydue to the combination of colloid- and polymer-like behaviors thatarise in these systems.We plan to explore the phase behavior and the material properties ofmicrogel suspensions at high concentration. Microgels offer theinteresting possibility to reach particle concentrations that aremuch higher than those that can be reached with hard spheres, asmicrogels deform easily, can interpenetrate and shrink, andtherefore, can fill space much more efficiently. So far, fundamentalproperties like their phase and non-equilibrium behavior are notwell known in this range of concentrations as a function of particlestiffness and swelling degree. Theoretical work suggests thatcrystal structures different from those of hard spheres should beexpected for particles that are not too soft, while very softparticles are predicted not to crystallize and to stay in the liquidstate. Furthermore, it has been shown that a large microgel particlein a crystal of small ones can shrink spontaneously to fit into thecrystal lattice to prevent the creation of a lattice defect -- abehavior that cannot occur in hard-sphere systems.The non-equilibrium behavior of microgel particles at highconcentrations is also far from understood, despite it has beenstudied to some extent with certain types of particles. In thesestudies, the microgel suspension falls out of equilibrium to becomea glass, like some molecular systems do. However, molecular glassformers exhibit a wide range of behaviors on their approach to theglass, which have no analogue in colloidal systems. Interestingly,recent experimental results with microgel suspensions have shownthat this wide range of behaviors is possible, although thereasons for why this is the case are still unclear and largelyunexplored.With this proposal, the experience and know-how of two laboratorieswith complemental facilities shall be combined to strengthen andexpand the ongoing collaboration on the properties of microgels athigh concentrations. The many unexplored aspects mentioned abovewill be tackled using a wide range of techniques such as directmeasurements of osmotic pressure, various scattering techniques, andreal space imaging, which are all available. Furthermore, the PhDstudent and the postdoc that we apply for shall profit from theinternational collaboration and the access to various experimentaltechniques.
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