Size and persistence length of molecular bottle-brushes by Monte Carlo simulations

Abstract

Single-chain simulations of densely branched comb polymers, or "molecular bottle-brushes" with side-chains attached to every (or every second) backbone monomer, were carried out by off-lattice Monte Carlo technique. A coarse-grained model, described by hard spheres connected by harmonic springs, was employed. Backbone lengths of up to 100 units were considered, and compared with the corresponding linear chains. The backbone molecular size was investigated as a function of its length at fixed arm size, and as a function of the arm size at fixed backbone length. The apparent swelling exponents obtained by a power-law fit were found to be larger than those for the corresponding linear polymers, indicative of stiffening of the comb backbone. The probability distribution function for the backbone end-to-end distance was also investigated for different backbone lengths and arm sizes. Analysis of this function yielded the critical exponents, which revealed an increase in the swelling exponent consistent with values found from the molecular size. The apparent persistence length of the backbone was also determined, and was found to increase with increasing branching density. Finally, the static structure factors of the whole bottle-brushes and of their backbones are discussed, which provides another consistent estimate of the swelling exponents.

Small Angle Neutron Scattering Study of Conformation of Oligo(ethylene glycol)-Grafted Polystyrene in Dilute Solutions: Effect of the Backbone Length

“…Methanol molecules have both hydrophilic hydroxyl groups and hydrophobic methyl groups; therefore, the PTrEGS polymers can also be easily dissolved in methanol. Figure 2 shows the SANS data of 1.0 wt % polymers with DP ) 85 in toluene-d 8 26 suggests that the interactions between the polymers in this solvent are attractive, and this is attributed to insolubility of hydrophobic PS backbones in water. Individual homopolymers such as PS are known to collapse into globules in poor solvents, and the globules tend to form clusters because of attractive interactions between polymer segments.…”

“…The nearly zero A 2 suggests that the solubility of the polymers in methanol is between toluene and D 2 O. The molecular weight of the polymer, M w , determined from Zimm plots in toluene-d 8 (27 800 g/mol), methanol-d 4 (39 600 g/mol), and in D 2 O (29 000 g/mol) agrees within 20% with the M w measured using gel permeation chromatography (34 800 g/mol). For the sake of clarity, the data of the toluene solutions were shifted by a factor of 1.2, 4, 8, 14, and 24 for the polymers of DP ) 8, 40, 47, 58, and 85, respectively.…”

“…[1][2][3][4][5][6][7][8][9][10] If side chains are long enough, then the backbone becomes highly extended because of the topological stiffness, 4 and the global conformation corresponds to that of a wormlike chain. Theoretical and computer simulation studies have focused on the wormlike chain regime where scaling relations between the persistence length, the length of the side chains, and the number of the side chains per backbone repeat unit are predicted; however, many of the theoretical predictions cannot be verified because of the limited amount of experimental data and availability of proper comblike polymers.…”

Molecular Dynamics Simulations of Bottle-Brush Polymers with a Flexible Backbone under Theta and Good Solvent Conditions

“…Therefore, it has recently been shown that the persistence length depends not onlyon the backbone length [19,20], but on the solvent conditions as well [15]. Although there exist many experimental and theoretical studies for the linear d imensions of these macro molecules in various solvents [3,4,19,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36],there are very few systematic studies of this problem [15], wherethe power laws and the associated effective exponents have been with a Flexible Backbone under Theta and Good Solvent Conditions discussed.It has been shown that for bottle brushes with a flexib le backbone evenat the theta point the side chains are considerably stretched,their linear dimension depending on the solvent quality only weakly, whilethe dependence of the persistence length on backbone length and temperature has alsobeen discussed [15].…”

Molecular dynamics simulations of single-component bottle-brush polymers with flexible backbones under poor solvent conditions

“…However, computer simulations have been very useful to validate approximations needed to interpret experimental data [10,12,16,17,18,19,20,21,22,23,24,25,26]. Since some of the suggested applications require to consider bottle-brush polymers under poor solvent conditions, first steps to consider this case by theory [27] and simulations [28,29,30] have been taken.…”