Onsets of Tethered Chain Overcrowding and Highly Stretched Brush Regime via Crystalline−Amorphous Diblock Copolymers

Abstract

Lamellar single crystals grown in dilute solutions can be used as templates for tethered chain analysis. Two series of diblock copolymers, poly(ethylene oxide)-block-polystyrene (PEO-b-PS) and poly(Llactic acid)-block-polystyrene (PLLA-b-PS), were used as model templates to generate tethered PS blocks on the single-crystal basal surfaces. Controlled and tunable reduced tethering density, σ ˜, defined by σπR g 2 (where σ is the tethered chain density and is equal to the reciprocal of the covered area of the chain and R g is the radius of gyration of this tethered chain in its end-free state at the same conditions), could be achieved in a broad range (up to 24) by changing the molecular weights (MW's) of the crystalline and amorphous blocks and by varying the crystallization temperature (T x ) of different PEO-b-PS and PLLA-b-PS solutions. For PEO and PLLA homopolymers crystallized in dilute solutions, the lamellar crystal thicknesses (d CRYST ) were observed to be proportional to the reciprocal undercooling ∆T (where ∆T ) T d -T x and T d is the equilibrium dissolution temperature of the crystals). The σ ˜of the tethered PS chains on the crystal surface increased with decreasing ∆T because at a fixed MW of the PEO or PLLA block, an increase in the d CRYST was evidence of a decrease in the number of folds. When we plotted the relationships between 1/d CRYST and T x for these two series of diblock copolymers, sudden and discontinuous changes of the slopes in some of these were observed at σ ˜) 3.7 (σ ˜*). This was as a result of the drastic interaction change of the neighboring PS tethered chains. An average reduced surface free energy of the tethered PS chains (Γ PS ) was defined and used as a parameter to characterize the PS tethered chain interactions. The relationship between Γ PS and σ ˜showed a discontinuous transition at σ ˜*, which had a close similarity to the hard-sphere-like interaction model. This could be identified as the onset of the tethered PS chain overcrowding in solution. This transition indicates that the extra entropic surface free energy created by the repulsion of tethered PS chains started to affect the nucleation barrier of the PEO or PLLA block crystallization. On the basis of the scaling laws, the onset of highly stretched brush regime could be identified at σ ˜) 14.3 (σ ˜**). In the Γ PS vs σ ˜plot, the transition appears to be continuous. Thus, a crossover regime in the tethered PS chains exists between σ ˜* ) 3.7 and σ ˜** ) 14.3. It is defined as the regime where the interaction of the tethered PS chains undergoes changes from being noninteracting toward penetration to, finally, chain stretching normal to the surface.

Fine fibrillar and rectangular/hexagonal ordered grains of poly(3-hexyl thiophene) and poly(ethylene glycol) developed by seeding technique

“…In our work, the lens-shaped crystals were also observed for the homo-PEG 5000 . The lens-shaped crystals were previously reported for PS-b-PEO by Zheng and co-authors [55].…”

“…In conclusion, the relation applied for the grafting density of conventional homo-brush single crystals (Eq. 2) [55] was not more usable for the random single-cocrystals.…”

“…3) [18,55], and the molecular weight of PEG (=5000 g/cm 3 ), respectively. Equation (2) was only applicable for the systems, in which all contributing chains in the single crystal structure had the amorphous blocks.…”

Two-dimensional assemblies from crystallizable homopolymers with charged termini

“…13,29 Furthermore, to our knowledge, the use of different seeds from the same polymer to induce the formation of 2D platelets of different shape via seeded growth in solution is unprecedented. Analysis by selected area electron diffraction (SAED) analysis revealed that the quasi-hexagonal disk-like and rectangular platelets (grown from 2D seedHD and 2D seedR1, respectively) have near identical ED patterns with three pairs of diffraction spots, confirming the presence of a single crystalline PFS core with monoclinic symmetry (Fig.…”

“…8,9 Recent advances have demonstrated the use of thiol-terminated crystalline homopolymers that allow the peripheral nanoparticle patterning on the 2D platelet, 10,11 as well as the fabrication of alternate rings of a homopolymer and BCP. 12,13 In a further advance, nanosheets formed by the crystallization of precursors containing silsesquioxane clusters bound to hyperbranched polymers can be fragmented into seeds using sonication which can be used to control the growth of 2D platelets on subsequent precursor addition. 14 We have shown that addition of a BCP with a crystallizable poly(ferrocenyldimethylsilane) (PFS) core-forming block 15 and a short complementary corona-forming block to seeds derived from the sonication of 1D cylindrical PFS BCP micelles allows access to lenticular platelet micelles.…”