Thermoresponsive PS-b-PNIPAM-b-PS Micelles: Aggregation Behavior, Segmental Dynamics, and Thermal Response

Abstract

We have studied the thermal behavior of amphiphilic, symmetric triblock copolymers having short, deuterated polystyrene (PS) end blocks and a large poly(N-isopropylacrylamide) (PNIPAM) middle block exhibiting a lower critical solution temperature (LCST) in aqueous solution. A wide range of concentrations (0.1−300 mg/mL) is investigated using a number of analytical methods such as fluorescence correlation spectroscopy (FCS), turbidimetry, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and neutron spin-echo spectroscopy (NSE). The critical micelle concentration is determined using FCS to be 1 μM or less. The collapse of the micelles at the LCST is investigated using turbidimetry and DLS and shows a weak dependence on the degree of polymerization of the PNIPAM block. SANS with contrast matching allows us to reveal the core−shell structure of the micelles as well as their correlation as a function of temperature. The segmental dynamics of the PNIPAM shell are studied as a function of temperature and are found to be faster in the collapsed state than in the swollen state. The mode detected has a linear dispersion in q 2 and is found to be faster in the collapsed state as compared to the swollen state. We attribute this result to the averaging over mobile and immobilized segments.

One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

“…The theoretically expected molar mass M n theo is calculated using eqn (6), where M CTA is the molar mass of the CTA, X is the conversion of the monomer, M DMA is the molar mass of the monomer and n is the number of moles, respectively:…”

“…Typical rheology modifiers used are a,u-double hydrophobically end-capped hydrophilic polymers. [1][2][3][4][5][6][7][8][9][10][11] So far, these have been mostly polyethylene oxides (PEOs) end-capped with n-alkyl ethers, n-alkyl urethanes (HEURs), and fatty acid esters or, alternatively, PEOs bearing short hydrophobic polymer end blocks. 8 The thickening effect of these compounds has been studied intensely.…”

Recent progress on polymer dynamics by neutron scattering: From simple polymers to complex materials

“…53 Finally, hydrated polymers and polymer solutions-in particular, microgels-have also recently been investigated by QENS. [54][55][56][57][58][59][60][61][62][63] Studies on concentrated aqueous solutions show that confinement effects also arise -in this case for the minority water component-when the polymer freezes approaching its glass-transition. The component dynamics in these solutions can be selectively monitored by QENS, a task that is not easily achievable by other usually applied experimental approaches like, for example, dielectric spectroscopy.…”

“…Some of them have been extensively investigated by several techniques including SANS (of utmost interest to characterize the structural changes across the transition) and QENS. First QENS reports on a slowing down of the dynamics at the VPTT were based on the local dynamics investigations by Rubio-Retama et al 157,158 Aqueous (D 2 O) solutions of triblock copolymers P(S-b-NIPAM-b-S) were recently studied by Adelsberger et al 59 The polymer forms micelles with a rigid PS core and a PNIPAM shell, that aggregate in clusters right after the collapse temperature is crossed. Using samples with deuterated PS blocks, the scattering from the solvent was matched and NSE revealed the PNIPAM dynamics.…”

From UV to NIR light, photo-triggered 1,3 dipolar cycloadditions as a modern ligation method in solution and on surface

“…Furthermore, the RAFT process can be utilized for synthesis of the desired macromolecular architecture. 58 A large range of polymer structures synthesized via RAFT approach is established, including block copolymers for micelle formation, [59][60][61][62] brush-, 63 comb-, 64 and star [65][66][67] polymers.…”