MSc Thesis Presentation: Dynamical self-consistent field theory simulation of high-generation, dendritic phytoglycogen nanoparticles

MSc Candidate

Benjamin Morling

Abstract

Phytoglycogen  (PG)  is  a  naturally  occurring,  highly  branched,  glucose  dendrimer  that  is  extracted  from  sweet  corn  as  soft,  compact,  22  nm  radius  nanoparticles.  Extensive  experimental  studies  have  been  performed  to  characterize the structural and hydration properties of PG nanoparticles; however, little work has been done to develop a realistic, yet efficient, model of PG that can help interpret previous experimental results, and direct new avenues for experimental investigation. The purpose of the work in this thesis is to develop an efficient model of a PG nanoparticle solubilized in water using dynamical self-consistent field theory (dSCFT). In dSCFT, a saddle-point approximation to the dynamical partition function of the system reduces the problem of the dynamics of pairwise interacting coarse-grained dendrimer and solvent beads to that of the evolution of these beads in self-consistently determined dynamical mean-force fields. To introduce further efficiency into the evolution of the 11-generation dendrimer with N≈18,500 coarse-grained beads, we exploit the hierarchical dendritic architecture of PG  to  decompose  the  bead-spring  dynamics  of  the  entire  dendrimer  into  the  independent  dynamics  of  its  constituent  sub-chains.  We  show  that  decomposing  the  bead-spring  dynamics  of  the  dendrimer  in this  manner  produces  a  stable  bond  evolution  algorithm  that  has  a  power  of  N  improvement  in  the  run-time  scaling  with  increasing dendrimer size over the standard algorithm while introducing negligible error. By varying the strength of the interactions between the PG nanoparticle and water, we are able to tune both the size and hydration of the nanoparticle to agree with the values measured using small-angle neutron scattering (SANS).  We show that our model  successfully  captures  the  dense  spherical  core  and  diffuse  outer  chain  morphology  of  PG  nanoparticles  inferred  from  SANS,  rheology,  and  atomic  force  microscopy  measurements.    This  thesis  serves  as  both  a  qualitative  and  quantitative  validation  of  our  dSCFT  model  of  PG  in  addition  to  laying  the  groundwork for modeling modified versions of PG nanoparticles currently under experimental investigation.

Examination Committee

• Dr. Eric Poisson, Chair
• Dr: John Dutcher, Advisor
• Dr. Robert Wickham, Co-Advisor 
• Dr. Alexandros Gezerlis, Advisory Committee