My research focuses on the exploitation of combining different neutron scattering techniques with different time and spatial scales, with molecular dynamics simulations, to better understand the dynamics in Soft Matter systems. Neutron scattering is an ideal tool since it is non-destructive, neutrons are highly penetrating, and probes atomic/molecules lengthscales and timescales which overlap with that from simulations. More specifically I am interested in the dynamics of polymeric and biological systems.
V García Sakai, C. Alba-Simionesco, S.-H. Chen [Eds.], Dynamics of Soft Matter, Springer, New York, 2012
V García Sakai and A. Arbe, Quasielastic neutron scattering in soft matter, Current Opinion in Colloid & Intefrace Science 14 (2009) 381-390
Trehalose, a disaccharide found in organisms that survive desiccation over long periods of time, is known to have a stabilizing effect on biologicals and is used for the long-term storage of membranes, proteins and cells. For membranes, trehalose lowers the melting temperature of the bilayer preventing leakage during freezing and drying of cells. For low temperature storage, glycerol appears to be a better candidate. In both cases though, the mechanism underlying stabilization is still not well understood.
V. García Sakai, S. Khodadadi, M. T. Cicerone, J. E. Curtis, A. P. Sokolov, J. Ho Roh, Solvent effects on protein fast dynamics:implications for biopreservation,Soft Matter Communication 9 (2013) 5336-5340
M Doxastakis, V. García Sakai, S. Ohtake, J.K. Maranas, J.J. de Pablo, A molecular view of melting in anhydrous phospholipidic membranes, Biophys J 92 (2007) 147
Dynamics of biological macromolecules
The dynamics of biological macromolecules span many orders of magnitude, and in addition to their structure play a key role in their function in living organisms. Understanding the dynamics of functional groups in protein as a function of hydration, pH and environment in general will help us understand how proteins function. In particular membrane proteins represent a important research challenge, since they participate in many life processes. Protein-protein interactions, lipid-protein interaction, lipid matrix behavior are all integral parts; an understanding of the dynamics in these systems in combination with structural studies should give us a complete picture.
L Toppozini, CL Amstrong, MA Barett, S Zheng, L Luo, H Nanda and V Garcia Sakai, Partitioning of Ethanol into Lipid Membranes and its Effect on Fluidity and Permeability as seen by X-ray and Neutron Scattering, Soft Matter 8 (2012) 11839-11849
VK Sharma, S Mitra, V García Sakai, PA Hassan, J Peter Embs, R Mukhopadhyay, The dynamical landscape in CTAB micelles, Soft Matter 8, 3151-3160 (2012)
SV Ghugare, E Chiessi, B Cerroni, MTF Telling, V García Sakai, G Paradossi, Biodegradable dextran based microgels: a study on network associated water diffusion and enzymatic activity, Soft Matter 8 (2012) 2494-2
MFT Telling, C Neylon, L Clifton, WS Howells, L van Eijck, V García Sakai, Thermal motion in the multi-subunit protein, apoferritin, as probed by high energy resolution neutron spectroscopy, Soft Matter 7 (2011) 6934-6941
Y Gerelli, V García Sakai, J. Ollivier, A Deriu, Conformational and segmental dynamics in lipid-based vesicles, Soft Matter 7 (2011) 3929-3935
VK Sharma, G Verma, PA Hassan, V García Sakai, R Mukhopadhay, Internal dynamics in SDS micelles: neutron Scattering study, J Phys Chem B 114 (2010) 17049-17056
S Khodadadi, S Pawlus, JH Roh, V García Sakai, E. Mamontov, and A. P. Sokolov, The origin of the dynamic transition in proteins, J Chem Phys 128 (2008) 195106
G Caliskan, RM Briber, D Thirumalai, V. García Sakai, SA Woodson, AP Sokolov, Dynamic transition in tRNA is solvent induced , J Am Chem Soc 128 (2006) 32-33
Polymers for organic photovoltaics
Organic solar cells produce electricity from sunlight by means of conductive polymers. They provide a low-cost, light-weight, flexible alternative to both silicon and inorganic cells. Low-energy-gap congugated polymers such as poly-thiophenes have attracted much attention in recent years due to their electronic transport characteristics. Achieving high efficiencies, at least comparable to the 12-20% obtained with commercial inorganic cells, and long stability are two big research challenges. A deeper understanding of the relation between morphology, dynamics, and electronic properties will shed some light on the open questions about the transport properties and degradation processes of these materials.
Joint PhD student, Giuseppe Maria Paternò, with Prof. Franco Cacialli at UCL (London)
GM Paternò, F Cacialli, V. García Sakai, Structural and dynamical characterisation of P3HT/PCBM blends, Chem Phys SI (in press)
GM Paternò, F Cacialli, V. García Sakai, Micro-focused X-Ray Diffraction Characterization of High-quality [6,6]-Phenyl C61 Butyric acid Methyl Ester Single Crystals Without Solvent Impurities, J Mat Chem C (Communication) 1 (2013) 5619-5623.
C Díaz-Paniagua, A Urbina, V García Sakai, T Seydel, J Abad, J Padilla, R García-Valverde, N Espinosa, MJ Gómez-Escalonilla, F Langa, F Batallán, Molecular dynamics of solutions of poly-3-octyl-thiophene and
functionalized single wall carbon nanotubes studied by neutron
scattering, Chem Phys SI (in press).
Polymers in confinement
In order to create new materials with specific properties, we often rely on blending of two polymers or more recently on making nanocomposites. These have a very broad range of applications given their enhanced properties, but also provide very interesting fundamental science, that on confinement on the nanoscale. For example, blending two thermodynamically miscible polymers with vastly different glass transition temperatures (Tg) creates dynamical immiscibility, or understanding the reduction of Tg with the addition of nanoparticles similar to that observed in thin films.
P Akcora, SK Kumar, V García Sakai, LS Schadler, Segmental dynamics in PMMA-grafted nanoparticles, Macromolecules 43 (2010) 8275-8281
V. García Sakai, J. K. Maranas, I. Peral and J. R. D. Copley, Dynamics of PEO in blends with PMMA:Study of the effects of blend composition via QENS, Macromolecules 41 (2008) 3701
JM Kropka, V García Sakai, PF Green, Local polymer dynamics in polymer-C60 mixtures, Nano Letters 8 (2008) 1061
V García Sakai, JK Maranas, Z Chowdhuri, I Peral, JRD Copley, Miscible blend dynamics and the length scale of local compositions, J Polym Sci Polym Phys 43 (2005) 2914
V. García Sakai, J. K. Maranas, Z. Chowdhuri, Effect of blending with PEO on the dynamics of PMMA: A quasi-elastic neutron scattering approach, Macromolecules 37 (2004) 9975 .
V García Sakai, E Mamontov, DA Neumann, A Background Suppression Chopper for the High-Flux Backscattering Spectrometer at NIST, J Neutron Res 16 (2009) 65-74