Depth profile of the segmental dynamics at a poly(methyl methacrylate) film surface

Zuo, Biao; Liu, Yingjun; Wang, Lin; Zhu, Yiming; Wang, Yifan; Wang, Xinping

doi:10.1039/c3sm51658j

Cited by 45 publications

(53 citation statements)

References 83 publications

(124 reference statements)

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“…Proteins found on the solid-air interfaces of glassy lyophilized solids certainly experience an environment that is dramatically different from that inside the glass. 32 Effective glass transition temperatures are expected to be lower in the interfacial region than in the bulk, 33,34 allowing greater mobility for any protein molecules found at the surface of glassy lyophilized powders.…”

Section: Discussionmentioning

confidence: 99%

Protein Quantity on the Air–Solid Interface Determines Degradation Rates of Human Growth Hormone in Lyophilized Samples

Grobelny

Allmen

et al. 2014

Journal of Pharmaceutical Sciences

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rhGH was lyophilized with various glass-forming stabilizers, employing cycles that incorporated various freezing and annealing procedures to manipulate glass formation kinetics, associated relaxation processes and glass specific surface areas (SSA’s). The secondary structure in the cake was monitored by IR and in reconstituted samples by CD. The rhGH concentrations on the surface of lyophilized powders were determined from ESCA. Tg, SSA’s and water contents were determined immediately after lyophilization. Lyophilized samples were incubated at 323 K for 16 weeks, and the resulting extents of rhGH aggregation, oxidation and deamidation were determined after rehydration. Water contents and Tg were independent of lyophilization process parameters. Compared to samples lyophilized after rapid freezing, rhGH in samples that had been annealed in frozen solids prior to drying, or annealed in glassy solids after secondary drying retained more native-like protein secondary structure, had a smaller fraction of the protein on the surface of the cake and exhibited lower levels of degradation during incubation. A simple kinetic model suggested that the differences in the extent of rhGH degradation during storage in the dried state between different formulations and processing methods could largely be ascribed to the associated levels of rhGH at the solid-air interface after lyophilization.

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Section: Discussionmentioning

confidence: 99%

Protein Quantity on the Air–Solid Interface Determines Degradation Rates of Human Growth Hormone in Lyophilized Samples

Grobelny

Allmen

et al. 2014

Journal of Pharmaceutical Sciences

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“…Also using SFG technique, Tanaka et al 10 observed that the annealing temperature has a profound influence on the surface structure of PMMA and concluded that the backbone methylene groups became ordered at the surface after being annealed for long period of time at temperatures much higher than the glass transition temperature of PMMA. However, strong methylene resonance was also observed using as-spun PMMA samples by both Tanaka et al 11 and Wang et al, 23 which suggested the high-temperature annealing was not necessary for ordering the methylene groups. In addition, no methylene resonance was observed in studies by Somorjai et al 13 and Chou et al 24 in which PMMA samples have been annealed at or above 100°C.…”

Section: ■ Introductionmentioning

confidence: 91%

Molecular Structure of Poly(methyl methacrylate) Surface II: Effect of Stereoregularity Examined through All-Atom Molecular Dynamics

et al. 2014

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The chemical composition and molecular structure of polymeric surfaces are important in understanding wetting, adhesion, and friction. Here, we combine interfacesensitive sum frequency generation spectroscopy (SFG), allatom molecular dynamics (MD) simulations, and ab initio calculations to understand the composition and the orientation of chemical groups on poly(methyl methacrylate) (PMMA) surface as a function of tacticity and temperature. The SFG spectral features for isotactic and syndiotactic PMMA surfaces are similar, and the dominant peak in the spectra corresponds to the ester-methyl groups. The SFG spectra for solid and melt states are very similar for both syndiotactic and isotactic PMMA. In comparison, the MD simulation results show that both the ester-methyl and the α-methyl groups of syndiotactic-PMMA are ordered and tilted toward the surface normal. For the isotactic-PMMA, the α-methyl groups are less ordered compared to their ester-methyl groups. The backbone methylene groups have a broad angular distribution and are disordered, independent of tacticity and temperature. We have compared the SFG results with theoretical spectra calculated using MD simulations and ab initio calculations. Our analysis shows that the weaker intensity of α-methyl groups in SFG spectra is due to a combination of smaller molecular hyperpolarizability, lower ordering, and lower surface number density. This work highlights the importance of combining SFG spectroscopy with MD simulations and ab initio calculations in understanding polymer surfaces. ■ INTRODUCTIONOne of the simplest and still commonly used technique to characterize surfaces of polymers is the measurement of water contact angle. Although this is a very simple technique to judge the wettability of surfaces, it lacks molecular level sensitivity to identify the chemical composition and molecular structure of surfaces. In addition, the rearrangement of molecules at the surface after exposure to water complicates the interpretation of contact angle results. 1 X-ray photoelectron spectroscopy (XPS), a vacuum-based technique, provides excellent information regarding the elemental composition present at the surfaces. However, to identify different hydrocarbon groups (or bondings) is not trivial and relies on subtle shifts of carbon binding energies in the high-resolution XPS analysis. 2 Attenuated-total-reflectance infrared can be used to pick up molecular fingerprints, but this technique samples a much thicker layer than the surface region that affects wetting, surface energy, and friction. 3 In the past two decades, surface-sensitive infrared−visible sum frequency generation spectroscopy (SFG) has been used to study polymer surfaces, 4−7 polymer/liquid interfaces, 7−11 polymer/metal or metal oxide interfaces, 5,12−15 and polymer/polymer interfaces. 12,16−19 SFG is a second-order nonlinear optical technique, and under electric dipole approximation, the SFG signal is only generated by the ordered molecules at surfaces or interfaces and the contribution from ...

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“…The dense smooth lms were prepared via a drop-casting method and annealing at 105 C for 24 h to drive the low surface energy components, uorinated groups or alkyl groups, to segregate on the lm surface to satisfy the thermodynamic requirements for a minimal surface free energy. 54 It can be seen that the water and oil contact angles gradually increase with increasing alkyl chain length and the number of uorine atoms; accordingly, the free surface energies exhibit a reverse trend. In addition, it is reasonable that polystyrenes with uorinated end groups possess lower surface free energies than those with alkyl end groups.…”

Section: Interfacial Activity Of the Chain-end-functionalized Polysty...mentioning

confidence: 98%

Polystyrene with hydrophobic end groups: synthesis, kinetics, interfacial activity, and self-assemblies templated by breath figures

Zhu

Wan

et al. 2014

Polym. Chem.

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The breath figure method has emerged as a new self-assembly technique to fabricate ordered porous materials, which show potential applications in many fields, such as size-selective separation membranes. However, it is challenging to customize the structures, especially to precisely tune the pore size in a wide range. Moreover, the relationship between polymer structure and film morphologies is still unknown. In this paper, we report a facile, effective, and controllable way to manipulate the evolution of morphologies of honeycomb films, which is based on the blends of an amphiphilic block copolymer and polystyrenes with hydrophobic end groups. A series of atom transfer radical polymerization (ATRP) initiators with alkyl or fluorinated groups were synthesized for polystyrenes with hydrophobic end groups. Polymerization kinetics confirmed the viability of these ATRP initiators. Surface segregation behaviors of the hydrophobic end groups were demonstrated by measuring the surface chemical composition and surface free energies. We found that the polystyrenes with hydrophobic end groups form ordered films only at high polymer concentration (40-60 mg mL À1 ); moreover, the use of blends of two types of polystyrenes, one of which has a hydrophobic end group whereas the other has a hydrophilic block, can greatly increase the regularity of the honeycomb films and provide the possibility to fine-tune the pore diameter. Moreover, the evolution of surface morphologies of the films can be ideally correlated with the surface free energies of the end-functionalized polymers.

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Depth profile of the segmental dynamics at a poly(methyl methacrylate) film surface

Cited by 45 publications

References 83 publications

Protein Quantity on the Air–Solid Interface Determines Degradation Rates of Human Growth Hormone in Lyophilized Samples

Protein Quantity on the Air–Solid Interface Determines Degradation Rates of Human Growth Hormone in Lyophilized Samples

Molecular Structure of Poly(methyl methacrylate) Surface II: Effect of Stereoregularity Examined through All-Atom Molecular Dynamics

Polystyrene with hydrophobic end groups: synthesis, kinetics, interfacial activity, and self-assemblies templated by breath figures

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