PD Dr. Urs Gasser

My research focuses on fundamental aspects in soft condensed matter physics, in particular the rich behavior of polymers and colloidal suspensions. Soft matter materials have building blocks with sizes in the nano- to micrometer range with interactions on the order of thermal energy as in atomic or molecular materials. However, the interaction energy per volume is much lower such that soft matter is often easy to deform or compress with elastic moduli on the order of 1 to 10 Pascals.
Soft matter shows a wide range of material properties and bulk behaviors beyond the well known phase behavior of atomic and molecular substances. The reason for the diversity of soft matter stems from the dependence of the constituent interactions on the size, the surface and bulk properties, the geometrical shape of the constituents, and the properties of the solvent in the case of colloids.

My four main research areas are:
• Crystal nucleation and growth in colloidal model systems.
• Interactions and phase behavior of soft colloidal particles.
• Phase behavior of mixtures of magnetic and non-magnetic colloids.
• Morphology and functional properties of grafted copolymer membranes for fuel cells.

My primary tools are small-angle neutron and X-ray scattering, light scattering, as well as real space imaging (optical microscopy).

Phase behavior of binary and polydisperse suspensions of compressible microgels controlled by selective particle deswelling
A. Scotti, U. Gasser, E.S. Herman, Jun Han, A. Menzel, L.A. Lyon, and A. Fernandez-Nieves
Phys. Rev. E96, 032609 (2017).

Small-angle neutron scattering to unravel the selective deswelling of microgel particles
A. Scotti, U. Gasser, L.A. Lyon, and A. Fernandez-Nieves
Swiss Neutron News50, 14-21 (2017).

Radiation grafted ion-conducting membranes: The influence of variations in base film nanostructure
V. Sproll, G. Nagy, U. Gasser, J.P. Embs, M. Obiols-Rabase, T.J. Schmidt, L. Gubler, and S. Balog
Macromolecules49, 4253-4264 (2016).

The role of ions in the self-healing behavior of soft particle suspensions
A. Scotti, U. Gasser, E.S. Herman, M. Pelaez-Fernandez, J. Han, A. Menzel, L.A. Lyon, and A. Fernandez-Nieves
PNAS113, 5576-5581 (2016).

Structure-property correlations of ion-containing polymers for fuel cell applications
V. Sproll, G. Nagy, U. Gasser, S. Balog, S. Gustavson, T.J. Schmidt, L. Gubler
Radiation Physics and Chemistry118, 120-123 (2016).

The CONTIN algorithm and its application to determine the size distribution of microgel suspensions
A. Scotti, W. Liu, J.S. Hyat, E.S. Herman, H.S. Choi, J.W. Kim, L.A. Lyon, U. Gasser, A. Fernandez-Nieves
The Journal of Chemical Physics142, 234905 (2015).

Form factor of pNIPAM microgels in overpacked states
U. Gasser, J.S. Hyatt, J.-J. Lietor-Santos, E.S. Herman, L.A. Lyon, A. Fernandez-Nieves
The Journal of Chemical Physics141, 034901 (2014).

Structure of the aqueous phase and its impact on the conductivity of graft copolymer ionomers at saturation
S. Balog, K. Jetsrisuparb, U. Gasser, G.G. Scherer, L. Gubler
Polymer55, 3026-3036 (2014).

A novel method of extraction of blend component structure from SANS measurements of homopolymer bimodal blends
O. Smerdova, R.S. Graham, U. Gasser, L.R. Hutchings, D.S.A. De Focatiis
Molecular Chemistry and Physics215, 859-866 (2014).

Characterization of local structures with bond-order parameters and graphs of the neares neighbors, a comparision
U. Gasser, F. Ziese, G. Maret
Eur. Phys. J. Special Topics223, 455-467 (2014).

Transient formation of bcc crystals in suspensions of poly(N-isopropylacrylamide)-based microgels
U. Gasser, J.-J. Lietor-Santos, A. Scotti, O. Bunk, A. Menzel, A. Fernandez-Nieves
Phys. Rev. E88, 052308 (2013).

Heterogeneous nucleation and crystal growth on curved surfaces observed by real-space imaging
F. Ziese, G. Maret, and U. Gasser
J. Phys.: Condens. Matter25, 375105 (2013).

Structure of the hydrophilic phase and its impact on the conductivity of graft copolymer ionomers at low hydration level
S. Balog, U. Gasser, K. Jetsrisuparb, L. Gubler
Polymer54, 4266-4275 (2013).

Ellipsoidal hybrid magnetic microgel particles with thermally tunable aspect ratios
V. Städele, U. Gasser, H. Dietsch
Soft Matter8, 4427-4431 (2012).

Structure of the ion-rich phase in DVB cross-linked graft-copolymer proton-exchange membranes
S. Balog, U. Gasser, K. Mortensen, H. Ben Youcef, L. Gubler, and G. G. Scherer
Polymer53 (1), 175-182 (2012).

Nano-scale morphology in graft copolymer proton-exchange membranes cross-linked with DIPB
S. Balog, U. Gasser, K. Mortensen, H. Ben Youcef, L. Gubler, and G. G. Scherer
Journal of Membrane Science383, 50-59 (2011).

The effect of hydrostatic pressure over the swelling of microgel particles
J.J. Lietor-Santos, B. Sierra-Martin, U. Gasser, and A. Fernandez-Nieves
Soft Matter7, 6370-6374 (2011).

Magnetic properties of silica coated spindle-type hematite particles
M. Reufer, H. Dietsch, U. Gasser, B. Grobety, A.M. Hirt, V.K. Malik, and P. Schurtenberger
J. Phys.: Condensed Matter23, 065102 (2011).

Structural changes of poly(N-isopropylacrylamide)-based microgels induced by hydrostatic pressure and temperature studied by small angle neutron scattering
J.-J. Lietor-Santos, U. Gasser, R. Vavrin, Z.B. Hu, and A. Fernandez- Nieves
The Journal of Chemical Physics133, 034901 (2010).

Crystal structure of highly concentrated, ionic microgel suspensions studied by small angle X-ray scattering
U. Gasser, A. Fernandez-Nieves
Phys. Rev. E81, 052401 (2010).

Morphology and Ori- entational Behavior of Silica-Coated Spindle-Type Hematite Particles in a Magnetic Field Probed by Small-Angle X-ray Scattering
M. Reufer, H. Dietsch, U. Gasser, A. Hirt, A. Menzel, and P. Schurten- berger
J. Phys. Chem. B114, 4763-4769 (2010).

Melting of Crystals in Two Dimensions
U. Gasser, C. Eisenmann, G. Maret, and P. Keim
ChemPhysChem11, 963-970 (2010).

Correlation between Morphology, Water Uptake, and Proton Conductivity in Radiation Grafted Proton Exchange Membranes
S. Balog, U. Gasser, K. Mortensen, L. Gubler, H. Ben youcef, and G. G. Scherer
Macromolecular Chemistry & Physics211, 635-643 (2010).

Neutrons for Fuel Cells
S. Balog, U. Gasser, P. Boillat, P. Oberholzer, G. G. Scherer, E. Lehmann, and K. Mortensen
Swiss Neutron News38, 4-13 (2010).

Deswelling Microgel Particles Using Hydrostatic Pressure
J.-J. Lietor-Santos, B. Sierra-Martin, R. Vavrin, Z. Hu, U. Gasser, and A. Fernandez-Nieves
Macromolecules42, 6225-6230 (2009).

Crystallization in three- and two-dimensional colloidal suspensions
U. Gasser
J. Phys.: Condensed Matter21, 203101 (2009).

Crystal structure of highly concentrated, ionic microgel suspensions studied by neutron scattering
U. Gasser, B. Sierra-Martin, and A. Fernandez-Nieves
Phys. Rev. E79, 051403 (2009).

Structural Characterization of Radiation-Grafted Block Copolymer Films, Using SANS Technique
K. Mortensen, U. Gasser, S. Alkan Gürsel, and G.G. Scherer
Journal of Polymer Science: Part B: Polymer Physics46, 1660 (2008).

Spinodal decomposition in a model colloid-polymer mix- ture in microgravity
B.A.E. Bailey, W.C.K. Poon, R.J. Christianson, A.B. Schofield, U. Gasser, V. Prasad, S. Manley, P.N. Segre, L. Cipelletti, W.V. Meyer, M.P. Do- herty, S. Sankaran, A.L. Jankovsky, W.L. Shiley, J.P. Bowen, J.C. Eggers, C. Kurta, T. Lorik, P.N. Pusey, and D.A. Weitz
Phys. Rev. Lett.99, 205701 (2007).

Noncentral Forces in Crystals of Charged Colloids
D. Reinke, H. Stark, H.-H. von Grünberg, A. Schofield, G. Maret, and U. Gasser
Phys. Rev. Lett.98, 038301 (2007).

Pair Interaction of Dislocations in Two-Dimensional Crystals
C. Eisenmann, U. Gasser, P. Keim, G. Maret, and H.H. von Grünberg
Phys. Rev. Lett.95, 185502 (2005).

Colloidal layers in magnetic fields and under shear flow
H. Löwen, R. Messina, N. Hoffmann, C.N. Likos, C. Eisenmann, P. Keim, U. Gasser, G. Maret, R. Goldberg, and T. Palberg
J. Phys.: Condensed Matter17, S3379 (2005).

Time-Dependent Strength of Colloidal Gels
S. Manley, B. Davidovitch, N.R. Davies, L. Cipelletti, A.E. Bailey, R.J. Christianson, U. Gasser, V. Prasad, P.N. Segre, M.P. Doherty, S. Sankaran, A.L. Jankovsky, B. Shiley, J. Bowen, J. Eggers, C. Kurta, T. Lorik, and D.A. Weitz
Phys. Rev. Lett.95, 048302 (2005).

Anisotropic mean-square displacements in two-dimensional colloidal crystals of tilted dipoles
V.A. Froltsov, C.N. Likos, H. Löwen, C. Eisenmann, U. Gasser, P. Keim, and G. Maret
Phys. Rev. E71, 31404-1-5 (2005).

Limits to Gelation in Colloidal Aggregation
S. Manley, V. Trappe, L. Cippelletti, A.E. Bailey, R.J. Christianson, U. Gas- ser, V. Prasad, P.N. Segre, M.P. Doherty, S. Sankaran, A.L. Jankovsky, B. Shiley, J. Bowen, K. Dendorfer, J. Eggers, C. Kurta, T. Lorik, P.N. Pusey, and D.A. Weitz
Phys. Rev. Lett.93, 108302-1-4 (2004).

Anisotropic defect mediated melting of two-dimensional colloidal crystals
C. Eisenmann, U. Gasser, P. Keim, and G. Maret
Phys. Rev. Lett.93, 105702-1-4 (2004).

Melting of anisotropic colloidal crystals in 2D
C. Eisenmann, P. Keim, U. Gasser, and G. Maret
J. Phys.: Condensed Matter16, S4095-S4102 (2004).

Local order in a supercooled colloidal fluid observed by confocal microscopy
U. Gasser, A. Schofield, and D.A. Weitz
J. Phys.: Condensed Matter15, 375-380 (2003).

Real-Space Imaging of Nucleation and Growth in Colloidal Crystallization
U. Gasser, Eric R. Weeks, Andrew Schofield, P.N. Pusey, and D.A. Weitz
Science292, 258-262 (2001).