Molecular Weight Dependence Research Articles

Stochastic simulation of pattern formation in electron beam lithography

A molecular scale simulation of the pattern formation process in electron beam lithography based on the stochastic approach is proposed. The formation of the initial resists structure is achieved by sequentially joining randomly selected monomers. The effects of electron exposure for positive-type resists are introduced by scission of the polymer chain. The effects of electron exposure for negative-type resists are introduced by crosslinkings among the polymer chains. The fundamental properties, such as sensitivity curves, molecular weight dependence, and exposure condition effects on pattern profiles, are well reproduced by the simulation. The simulation results are shown to be appropriate when compared with the properties reported from the experiment.

Fluorescent and molecular weight dependence of THM and HAA formation from intracellular algogenic organic matter (IOM)

This study (i) examined the formation of two major carbonaceous disinfection by-products (C-DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), during the chlorination of intracellular algogenic organic matter (IOM) extracted from two commonly blooming algae M. aeruginosa (MA) and Chlorella sp. (CH), and (ii) investigated the roles and relationships of fluorescent and molecular weight (MW) properties on/with IOM-derived THMs and HAAs. The extracted IOM samples were separated into different MW fractions by centrifugal devices with membrane support with MW cut-offs of 100, 30, 10, 3, and 1 kDa. We observed an overall reduction of C-DBPs with a decrease of IOM-MW from >100 kDa to <1 kDa. Of six fractionated IOM, a large fraction (>100 kDa) contributed the largest amount to the MW distribution of IOM, accounting for 33 and 42% of the total dissolved organic carbon (DOC) of MA and CH, respectively. It also had the highest-yielding potential to produce significant levels of THMs and HAAs, and total C-DBPs over other small MW fractions. Although small MW fractions (>10 kDa) contributed around 50% of the total DOC, they made an insignificant contribution (>20%) to the THMs, HAAs, and overall C-DBPs. Furthermore, the decrease of IOM MW caused a shift from the domination of HAA formation to THM formation, especially when MW was <10 kDa. By canonical correspondent analysis, the relationship of IOM-derived THMs and HAAs with IOM properties was examined. In particular, large fractions of IOM, exhibiting aromatic protein- (AP) and soluble microbial product- (SMP) like fluorescence, are favorable for the formation of HAAs, whereas small MW fractions of IOM with HA- and FA-like fluorescence preferentially tends to form THMs. Our findings evidently show the strong dependence of IOM-derived THMs and HAAs on the fluorescent and MW properties. Therefore, the characterization of MW and fluorescent properties can provide the advantages in the control of algae-derived DBPs upon the chlorination of eutrophic water.

Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution.

Reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate was used to prepare three poly(glycerol monomethacrylate)x–poly(2-hydroxypropyl methacrylate)y (denoted Gx-Hy or PGMA-PHPMA) diblock copolymers, namely G37-H80, G54-H140, and G71-H200. A master phase diagram was used to select each copolymer composition to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies. The latter technique indicated a mean worm cross-sectional diameter (or worm width) ranging from 11 to 20 nm as the mean degree of polymerization (DP) of the hydrophobic PHPMA block was increased from 80 to 200. These copolymer worms form soft hydrogels at 20 °C that undergo degelation on cooling. This thermoresponsive behavior was examined using variable temperature DLS, oscillatory rheology, and SAXS. A 10% w/w G37-H80 worm dispersion dissociated to afford an aqueous solution of molecularly dissolved copolymer chains at 2 °C; on returning to ambient temperature, these chains aggregated to form first spheres and then worms, with the original gel strength being recovered. In contrast, the G54-H140 and G71-H200 worms each only formed spheres on cooling to 2 °C, with thermoreversible (de)gelation being observed in the former case. The sphere-to-worm transition for G54-H140 was monitored by variable temperature SAXS: these experiments indicated the gradual formation of longer worms at higher temperature, with a concomitant reduction in the number of spheres, suggesting worm growth via multiple 1D sphere–sphere fusion events. DLS studies indicated that a 0.1% w/w aqueous dispersion of G71-H200 worms underwent an irreversible worm-to-sphere transition on cooling to 2 °C. Furthermore, irreversible degelation over the time scale of the experiment was also observed during rheological studies of a 10% w/w G71-H200 worm dispersion. Shear-induced polarized light imaging (SIPLI) studies revealed qualitatively different thermoreversible behavior for these three copolymer worm dispersions, although worm alignment was observed at a shear rate of 10 s–1 in each case. Subsequently conducting this technique at a lower shear rate of 1 s–1 combined with ultra small-angle x-ray scattering (USAXS) also indicated that worm branching occurred at a certain critical temperature since an upturn in viscosity, distortion in the birefringence, and a characteristic feature in the USAXS pattern were observed. Finally, SIPLI studies indicated that the characteristic relaxation times required for loss of worm alignment after cessation of shear depended markedly on the copolymer molecular weight.

Expanding the application of the van Gurp-Palmen plot: New insights into polymer melt rheology

We report on an extension of the van Gurp-Palmen (vGP) plot [van Gurp, M. and Palmen, J., Rheology Bulletin, 1998, 67(1), 5–8.] developed through a compilation of literature data for polymer melts with different topological structures: linear (pure and blend), ring, comb, and bottlebrush. We introduce a new parameter: the reciprocal of complex modulus at the first minimum moving from the terminal regime (1/Gδmin,1∗) and compare it with the steady-state recoverable compliance Js. Results show that 1/Gδmin,1∗ and Js while related to each other in that they follow similar dependences on the molecular weight (linear and bottlebrush polymers), weight fraction of high molecular weight content (linear blends), and backbone concentration (comb polymer), there are also differences. For example, in the unentangled regime both Js and 1/Gδmin,1∗ increase with increasing molecular weight but reach different plateau values as entanglement coupling sets in. In the case of ring polymers, the molecular weight dependences of 1/Gδmin,1∗(∼Mw1) and Js(∼Mw2) show very different scaling with molecular weight and do not reach a plateau value even for molecular weights as high as approximately 15 times the entanglement molecular weight of the linear counterpart. Furthermore, examination of the impact of linear additives on the vGP plots of the rings potentially provides a new way to assess their freedom from linear contamination. Also, because 1/Gδmin,1∗ occurs in the frequency regime above that of the terminal regime and Js requires either very good estimates of terminal behavior in dynamic measurements or direct determination from creep and recovery measurements, 1/Gδmin,1∗ is easier to obtain. The work shows that detailed analysis of the van Gurp-Palmen plot has the potential to provide new insights into the rheological response of polymer melts over what is obtained conventionally from viscoelastic characterization methods.

Identification of LEA, a podocalyxin-like glycoprotein, as a predictor for the progression of colorectal cancer.

Large external antigen (LEA) is considered as a colorectal cancer (CRC)‐associated antigen, which was found via mAb ND‐1 generated using hybridoma technology, but its molecular features remain unknown. To facilitate the clinical application of LEA, we identified LEA as a podocalyxin‐like protein 1 (PODXL) with molecular weight of approximately 230 kDa, a hyperglycosylated protein, using immunoprecipitation and mass spectrometry in combination, and verified that ND‐1‐recognized epitope is on the terminal sialic acid of LEA. Correlation analysis between LEA and PODXL in molecular weight, immunological cross‐reactivity, and gene expression dependence supported the PODXL identity of the LEA. Moreover, we assessed the clinical significance of the LEA in 89 pairs of primary CRC tissues and adjacent nontumor colorectal tissues using ND‐1 by quantum dot‐based immunohistochemistry (QD‐IHC). High LEA expression was correlated significantly with T stage (P = 0.010). Patients with high LEA expression showed significantly poorer prognosis than those with LEA low expression (P = 0.007). Multivariate analysis indicated LEA expression as an independent predictor. Furthermore, the comparative analysis showed that mAb ND‐1‐based IHC analysis toward sugar residue of PODXL has higher sensitivity and specificity to evaluate the LEA/PODXL expression than mAb 3D3‐based method toward core protein of PODXL in CRC cell lines and clinical samples. In addition, we first found that LEA/PODXL can be secreted in exosomes from cancer cells and CRC patient peripheral blood. Our results demonstrate that LEA is an independent predictor for CRC progression and has the potential to be applied for clinical setting with high sensitivity, high specificity, and noninvasive access.

Molecular-weight dependence of phase structure and viscosity in a liquid crystalline polyester with strong π–π interaction

ABSTRACTIn this article, the molecular-weight dependence of the phase structure, rheological behaviour and thermal stability of a main-chain liquid crystalline polyester (PBDPS) with strong π–π interaction was investigated in details by differential scanning calorimetry, polarising optical microscopy, wide-angle X-ray diffraction, dynamic oscillatory rheological measurements and thermogravimetric analysis. While the molecular weight of PBDPS is 5.2k, it shows smectic B and smectic A phases prior to isotropic phase. With increasing molecular weight, smectic B phase of PBDPS gradually disappeared. Moreover, the smecitc B to smectic A (Tlc) and smectic A to isotropic (Ti) phase transition temperatures decreased as increased molecular weight. The rheology results suggested that fluid type of PBDPSs changed from Newtonian fluid to pseudo-plastic fluid as the molecular weight of PBDPS increased. In addition, the zero-shear viscosity (η0) of PBDPS showed a power law relationship () with molecular weight of PBDPS. All the PBDPSs showed good thermal stability with an initial decomposition temperature higher than 360°C.

Molecular weight dependence of chain conformation of strong polyelectrolytes.

Using sodium polystyrene sulfonate (NaPSS) and quarternized poly 4-vinylpyridine (QP4VP) as model systems, the chain conformation of polyelectrolytes under finite salt concentrations is investigated at a single molecular level. By fluorescence correlation spectroscopy (FCS), the hydrodynamic radius (R h) of the samples with the molecular weight ranging more than one order of magnitude was measured. The variations of R h as a function of molecular weight reveal the molecular weight dependence: under moderate salt concentrations (such as 10-4 and 0.1M), the shorter chains of both NaPSS and QP4VP take the rod-like conformation, while the longer chains take the coiled conformation (random coil or swelled random coil conformation, respectively). At high enough salt levels, both the charged chains take the coiled conformations. Photon counting histogram (PCH) measurements of the local pH value at the vicinity of the NaPSS chain expose the higher extent of counterion adsorption for longer chains as well as higher salt concentrations, telling that the charge regularization process is the major governing factor.

Surprising Temperature Scaling of Viscoelastic Properties in Polymers

We present detailed studies of segmental dynamics and viscosity in polystyrene (PS) and poly(2-vinylpyridine) (P2VP) with different molecular weights (MW). Analysis reveals that the molecular weight dependence exhibits very different temperature scaling for segmental and chain dynamics: while segmental relaxation in samples with different MW forms a master curve when presented vs T – Tg, the viscosity of the same samples falls on a master curve when presented vs Tg/T (here Tg is the glass transition temperature). This result indicates significant difference in the friction mechanisms for chain and segmental dynamics. Even more puzzling is that the absolute values of viscosity appear to be essentially MW independent when presented vs Tg/T up to surprisingly high molecular weight. In particular, viscosity at Tg does not show any appreciable molecular weight dependence up to MW ≈ 30 000 g/mol. We speculate that molecular scale relaxation (chain dynamics) in polymers behaves similar to the structural relaxati...

Molecular Dynamics of Polyfarnesene

This paper represents the first comprehensive report of the molecular weight dependence of the dynamics of polyfarnesene (PF), utilizing oscillatory shear rheology and broadband dielectric spectroscopy. Extended PF chain conformations arising from tightly packed C11/C13 pendant groups reduce the probability of chain entanglements and lead to Rouse-like melt dynamics up to a critical molecular weight ∼105 g/mol. At higher molecular weights, PF behaves as an entangled polymer melt. Dielectric spectroscopy measurements establish PF as a type-A polymer, whose normal mode relaxation is strongly dependent on molecular weight, providing a compliment to melt rheology for the exploration of PF global chain dynamics.

Study of phase separation behavior of poly(N,N-diethylacrylamide) in aqueous solution prepared by RAFT polymerization

A series of poly(N,N-diethylacrylamide) samples with low molecular weights (1.9 × 103–5.3 × 104) and narrow polydispersities (below 1.5 and usually lower than 1.25) was synthesized by reversible addition-fragmentation chain transfer polymerization. The phase separation behavior of poly(N,N-diethylacrylamide) in aqueous solution was investigated by turbidimetry, fluorescent probe technology and DSC. It is interesting to find that the lower critical solution temperature (LCST) of the samples increases with increasing molecular weight and remains more or less a constant above a critical molecular weight of 1.2 × 104. At the same time, an inverse dependence of LCST on the concentration was found and this effect was more pronounced for lower molecular weight. To further investigate the novel molecular weight dependence of the LCST, the fluorescent probe study was conducted and the experimental results demonstrated that there was an increase in hydrophobicity when decreasing the molecular weight and increasing the concentration and flower-like micelles were probably formed which can further be proved by TEM.

Insights into the Kinetics of the Resistance Formation of Bacteria against Ciprofloxacin Poly(2-methyl-2-oxazoline) Conjugates.

The influence on the resistance formation of polymers attached to antibiotics has rarely been investigated. In this study, ciprofloxacin (CIP) was conjugated to poly(2-methyl-2-oxazoline)s with an ethylene diamine end group (Me-PMOx28-EDA) via two different spacers (CIP modified with α,α'-dichloro- p-xylene-xCIP, CIP modified with chloroacetyl chloride-eCIP). The antibacterial activity of the conjugates against a number of bacterial strains shows a great dependence on the nature of the spacer. The Me-PMOx39-EDA-eCIP, containing a potentially cleavable linker, does not exhibit a molecular weight dependence on antibacterial activity in contrast to Me-PMOx27-EDA-xCIP. The resistance formation of both conjugates against Staphylococcus aureus and Escherichia coli was investigated. Both conjugates showed the potential to significantly delay the formation of resistant bacteria compared to the unmodified CIP. Closer inspection of a possible resistance mechanism by genome sequencing of the topoisomerase IV region of resistant S. aureus revealed that this bacterium mutates at the same position when building up resistance to CIP and to Me-PMOx27-EDA-xCIP. However, the S. aureus cells that became resistant against the polymer conjugate are fully susceptible to CIP. Thus, conjugation of CIP with PMOx seems to alter the resistance mechanism.

Reaction kinetics and simulations of ring-opening polymerization for the synthesis of polybutylene terephthalate

Cyclic polybutylene terephthalate (PBT) was polymerized with 2-ethylhexanoic acid tin(II) salt activated by 1-dodecanol in order to study the reaction mechanisms dominant in ring-opening polymerization (ROP) for polyester synthesis. Initiator-to-monomer content and temperatures were varied from 0.05% to 0.5% and 190 °C to 250 °C, respectively. The living-like character of ROP was confirmed by the characteristic effect of initiator content on cyclic oligomer conversion, along with the linear dependence of the number-average molecular weight upon conversion. The molecular weight distribution is mainly a function of the interplay between chain transfer and transesterification reactions. Since the PBT macrocycles appear in different sizes from 2 to 7 repeat units, each carbonyl group theoretically contributes to ring reactivity, where in this system both size-dependent and size-independent approaches to simulate propagation deliver appreciable results. The corresponding rate constants have been determined and, in contrast to other polymer systems, the proximity of these values to those of chain transfer and transesterification is significant.

Understanding the Molecular Weight Dependence of χ and the Effect of Dispersity on Polymer Blend Phase Diagrams

Gibbs ensemble Monte Carlo simulations and cloud point measurements were performed to understand the molecular weight dependence of χ and the effect of dispersity on the phase behavior of polymer mixtures. Oligomeric blends consisting of poly(ethylene-alt-propylene) (PEP) and poly(ethylene oxide) dimethyl ether (PEO) were used as the model systems. First, the molecular weight dependence of χ for PEP/PEO mixtures was studied using simulations and experiments for PEP/PEO mixtures with various molecular weights. An empirical model with a single adjustable parameter kij is used to quantify this molecular weight dependence, and it allows for the accurate prediction of χ of PEP/PEO mixtures with arbitrary molecular weights. Second, the effects of molecular weight distribution (MWD) and dispersity (Đ) of PEO on the PEP/PEO phase diagram were investigated via both simulations and experiments. When PEO is relatively monodisperse (Đ < 1.2), the phase diagram is found to be insensitive to either MWD or Đ, despite di...

Molecular-Weight Dependence of Nucleation Effect of a Liquid Crystalline Polyester β-Nucleating Agent for Isotactic Polypropylene

Unlike low-molecular-weight inorganic or organic nucleating agents (NAs), the physical properties, including phase transition and rheological behaviors, of polymeric NAs are greatly influenced by molecular weight. In this paper, the molecular-weight dependence of the β-nucleation behaviors of a polymeric NA (a main-chain liquid crystalline (LC) polyester, PBDPS) was studied in detail. The nucleation effect of PBDPS on isotactic polypropylene (iPP) shows a strong molecular-weight dependence. Low-molecular-weight PBDPS tended to induce the formation of α-iPP, whereas high-molecular-weight PBDPS tended to induce β-iPP. Moreover, the relative content of β-iPP crystals (kβ) first increased and then decreased as the molecular weight of PBDPS increased, with the maximum value (86.1%) obtained when 2 wt % PBDPS21.2k was incorporated. Furthermore, the stiffness, toughness, and heat distortion temperature (HDT) of iPP were simultaneously improved by incorporating PBDPS.

Molecular weight-dependent physisorption of non-charged poly(9,9-dioctylfluorene) onto the neutral surface of cuboidal γ-alumina in toluene

To understand how polymers physisorb onto solid surfaces, we investigated the physisorption behavior of non-charged, semiflexible poly(9,9-dioctylfluorene) (PF8) with three different number-average degrees of polymerization (DPn) as photoluminescent and chromophoric probes onto cuboidal γ-alumina in toluene at 5, 25, and 50 °C. PF8 revealed noticeable DPn and temperature dependencies in its physisorption behaviors. Molecular mechanics (MM)/molecular dynamics (MD) simulations [consistent valence force field (CVFF)] and Moller–Plesset second-order perturbation theory (MP2) with 6-31 G(d,p) calculations suggested that the PF8 in toluene has multiple interactions from CH/π to C–H/O interactions on the (110) surface of γ-alumina. The competition between multiple intermolecular CH/π and C–H/O interactions was crucial for the spontaneous physisorption of PF8 to occur in the presence of a solvent quantity of toluene. Calculations by time-dependent density functional theory (TD-DFT) with Becke three parameter Lee-Yang-Par (B3LYP) method and 6–31 G(d,p) basis set of a model fluorene 9-mer indicated that the π–π* absorption wavelength largely depends on the regularity of the dihedral angles between fluorene rings, while the intensity and spectral width of the π–π* absorption band are largely influenced by the regularity of the dihedral angles. Solution-phase physisorption systems are a result of the inherent nature of several competitive weak intermolecular interactions coexisting among the polymers, surface, and solvents. Noticeable molecular weight and temperature dependency for physisorption behavior of semiflexible, non-charged poly(9,9-n-dioctylfluorene) (PF8) onto cuboidal γ-alumina in toluene were found. MM/MD simulations (CVFF) and quantum mechanical (MP2/6-31G(d,p)) calculations suggested that PF8 swaps interacting toluene for (110) surface of γ-alumina by changing the interaction from CH/π interactions to C-H/O interactions of γ-alumina in toluene. The competition between multiple intermolecular CH/π and C-H/O interactions was crucial whether the spontaneous physisorption of PF8 occurs in place of solvent quantity of toluene. The solution-phase physisorption systems should be the consequence of several weak attractive intermolecular interactions coexisting between polymers, surface, and solvents

Self-assembly of nanoparticle-rich interphases in fiber reinforced polymeric composites using migrating agents

Thermoplastic additives, known as migrating agents, can be added to nanoparticle loaded thermosetting resins to form self-assembled nanoparticle structures. Most notably, in fiber reinforced thermosetting composites, self-assembled nanoparticle rich fiber-matrix interphases can be formed. While the self-assembly mechanism remains unclear, depletion interaction correctly describes the types of self-assembled structures formed. Formulations containing modest concentrations of migrating agent form self-assembled fiber-matrix interphases without causing aggregation in the bulk. Slight overdoses of migrating agent can lead to the formation of nanoparticle aggregates in the bulk phase, which can ultimately reduce the mechanical properties of the composite. Even larger overdoses of migrating agent cause the formation of large and open nanoparticle aggregates, indicative of rapid aggregation. Depletion theory predicts that larger molecular weight migrating agents should induce greater attractive forces, thus reducing the concentrations required to form these self-assembled structures. In this study, the migrating agent molecular weight dependence on the self-assembly and aggregation phenomenon are investigated. As predicted by depletion theory, larger molecular weights led to the formation of self-assembled interphases and aggregates at lower concentrations.

Anomalies in the coil-stretch transition of flexible polymers

The flow-induced coil-stretch transition of high molecular weight polymers has generally been held to be of first order. But evidence of significant slowing down in the rate at which the polymers relax to equilibrium in the vicinity of the transition suggests that the thermodynamic character of the transition may be less clear-cut. The above slowing down effect is actually characteristic of a second-order transition, and it points to the existence of a broad spectrum of conformational states in the transition region, analogous to the existence of fluctuations of all length scales at a critical point. In this paper, using a path integral approach based on a free-draining finitely extensible chain model, we calculate various polymer properties as a function of elongational flow as a way of exploring different statistical mechanical details of the coil-stretch transition. These properties include the molecular weight dependence of the flow-extension curve of the polymer, the distribution of its steady-state end-to-end distances, and the characteristic relaxation time τR of these distances. Among other findings, our calculations indicate that the coil-stretch transition is discontinuous in the N → ∞ limit, that the effective free energy of the chain is unimodal at all values of the flow, becoming broad and flat in the immediate vicinity of the transition, and that the ratio of τR to the Rouse relaxation time increases abruptly at the transition before eventually reaching a plateau value at large flow strengths. These aspects of the coil-stretch transition place it among a larger class of unconventional nominally first-order single chain transitions that include the adsorption transition of surface-tethered polymers and the escape transition of compressed polymers.

Crystallization and concentration fluctuation of miscible poly(vinylidene fluoride)/poly(methyl methacrylate) blends containing carbon nanotubes: Molecular weight dependence of poly(methyl methacrylate)

In this work, poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blend (50/50, wt/wt) and its blend composites containing carbon nanotubes (CNTs, 0.2 and 0.5 wt%) were prepared. Two types of PMMA with relatively large (PMMA-L) and small (PMMA-S) molecular weights were used to prepare the materials. It was observed that PVDF had higher crystallization ability in the samples containing PMMA-S. CNTs exhibited nucleation effect on the crystallization of PVDF and their nucleation efficiency was influenced by the molecular weight of PMMA. Rheological measurements showed that concentration fluctuation occurred during the melt annealing process even if the blend should be miscible at this temperature range, and more apparent concentration fluctuation was observed for the samples containing PMMA-S. Incorporating CNTs restrained the concentration fluctuation of the blend under the shear condition. Further results showed that larger concentration fluctuation in the melt state facilitated the higher crystallization ability of PVDF in the subsequent cooling process.

PH and molecular weight dependence of auric acid reduction by polyethylenimine and the gene transfection efficiency of cationic gold nanoparticles thereof

Small, cationic gold nanoparticles (GNPs) are produced by the direct reduction of auric acid in a non-reducing solvent, water, with branched polyethylenimine (bPEI) in a broad pH range (3.0–9.0).

Hydrodynamic interactions in DNA thermophoresis.

We theoretically study the molecular-weight dependence of DNA thermophoresis, which arises from mutual advection of the n repeat units of the molecular chain. As a main result we find that the dominant driving forces, i.e., the thermally induced permittivity gradient and the electrolyte Seebeck effect, result in characteristic hydrodynamic screening. In comparison with recent experimental data on single-stranded DNA (2 ≤ n ≤ 80), our theory provides a good description for the increase of the drift velocity up to n = 30; the slowing-down of longer molecules is well accounted for by a simple model for counterion condensation. It turns out that thermophoresis may change sign as a function of n: for an appropriate choice of the salt-specific Seebeck coefficient, short molecules move to the cold and long ones to the hot; this could be used for separating DNA by molecular weight.