The
conformational and thermodynamic properties of single dendritic–linear
copolymers are investigated by analytical models and computer simulations.
Applying poor solvent conditions on the dendritic part, these molecules
are known to form single unimolecular micelle-like structures. A mean-field
model applying the Daoud–Cotton approach and a surface tension
argument is presented and suggests the splitting of the unimolecular
single-core structure into a multicore structure with increasing dendrimers
generation and decreasing solvent selectivity. Monte Carlo simulations
utilizing the bond fluctuation model with explicit solvent are performed
which show the formation of multicore structures for trifunctional
codendrimers of different generations and spacer lengths with linear
chains attached to the terminal groups. These findings are aimed to
understand the physics of spontaneous self-assembly of codendrimers
in various well-defined macro-conformations under change of environmental
conditions with potential applications such as drug delivery systems.
We
study dendrimers embedded in a solution of linear chains with
various degrees of polymerization and concentrations. We distinguish
the term “crowding”, addressing the impact of the polymer
environment on the dendrimer, from the term “semidilute”,
which refers to the state of the polymer environment only. Depending
on the length of linear chains, two regimes are observed. Dendrimers
in a solution of chains much shorter then their own size display good
solvent characteristics at all concentrations. In a dense solution
of long chains the dendrimer conformation statistics changes qualitatively.
It displays Gaussian scaling with respect to the spacer length instead
of the cube root behavior expected for a compact globule. We have
found a very good description of the simulation data by using a geometrical
ansatz where for crowding given by the matching of the characteristic
length scales of the two subsystems; i.e., the ratio of the dendrimer
size and the correlation length of the semidilute solution provides
the relevant scaling variable. Our study reveals that dendrimer conformations
in the strongly crowed state neither are in a compact globular state
nor do they correspond to a mean-field θ-state. Instead, a novel
scaling variable combining the properties of both species reflects
the conformation statistics.
Semifluorinated (SF) side chain polymers show phase separation between polymer backbone and SF side chains. Due to strong interaction between SF segments the side chains determine the structure behaviour strongly, often resulting in layered structures in which backbones and layers of SF side chains alternate. The interest in this work was directed to find out the dependence of these structures on concentration of SF side chains. Thin films of random copolymers consisting of methylmethacrylate (MMA) and semifluorinated side chain methacrylate (SFMA) segments and with different fluorine content in the perfluoroalkyl side chains (abbreviated as H10F10 and H2F8) were prepared by spin-coating. Phase separation and structure changes were initiated by external subsequent annealing. Corresponding bulk material served as basic information. Generation of ordered structures and variation of film parameters were observed using different X-ray scattering methods (XRR, GIWAXS, and GISAXS). The phase behaviour in bulk is governed by the SF side chain amount and their specific fluorine content which control the self-organization tendency of SF side chains.Additionally, the confinement in thin films generates an orientation of side chains normally to film surface.
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