I joined ISIS as an instrument scientist for the neutron backscattering spectrometers IRIS and OSIRIS‚ in 2007. Prior to this I was an instrument scientist at the NIST‚ Center for Neutron Research in MD, USA. A chemical engineer by training at Imperial College London, I have concentrated my scientific career on understanding the behaviour of macromolecules, throughout my PhD at Imperial, my postdoc at Pennsylvania State University and my time at neutron facilities.‚
Research and development interests
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.
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.
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.
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) 2494-2502
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
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)
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
Professional activities: Memberships/External organisations
Associate Staff at University College London and London Center for Nanotechnology
Co-organiser of the Oxford School of Neutron Scattering (2011-present)
PhD Co-Supervisor of GMPaterno (with Prof. Franco Cacialli, UCL) - UCL Impact Studentship + ISIS
PhD Co-Supervisor of JM Hart (with Dr. R.Thompson Durham Univ and Prof. N Clarke Sheffield Univ) - STFC Futures Studenship
Member of the board of directors of the Sociedad Española de Técnicas Neutrónicas (2006‐present)
Member of the ILL Scientific Council (2014-2017)
Member of the ISIS Molecular Spectroscopy User Group Liason Team (2008‐2012)