Interchain Entanglements Research Articles

Analysis of structural changes during plastic deformations of amorphous polyethylene

Molecular dynamics (MD) simulations have been used to analyze yielding and stress-softening processes during stepped simple tensile loading of bulk amorphous polyethylene (PE) at temperatures (Tdef) well below the glass transition temperature (Tg). Specimens formed by 20 linear chains of 1000 beads each (2 × 104 coarse grained -CH2- units), with energetics described by a united atom potential, were deformed at Tdef = 100K. Configurations at axial strains (εxx) ranging from 0% to 30% were allowed to reach steady state equilibration. Subsequently, configurations in a time period of 5 ps were saved for analysis of their local structure. Local structural characteristics were analyzed using three methods: (i) a geometric description by computing the evolution of self and inter-chain entanglements, the number of bead contacts and the free volume, (ii) the method of Empirical Orthogonal Functions (EOF) to obtain a reduced description of the displacement field at each strain level and the vibration of each bead around its equilibrium position, and (iii) Hardy's method to compute the time averaged local stress tensor to obtain a detailed description of the distribution of internal forces. It was found that at early stages of deformation (εxx < 13%) the inter-chain entanglement continuously decreases while the self-entanglement showed no significant variation and no distinct patterning. Also the energy content in each eigenmode of the normalized displacement correlation matrix used in the EOF analysis is almost the same for a large portion of the frequency range regardless of the imposed axial strain level. Furthermore, distribution of the local pressure presented a positive expected value at the initial (εxx = 0%) configuration; the expected value continuously decreases toward the point where the axial stress peaks (εxx = 13%). The evolution of the number of loosely packed regions (quasi-defects), identified by a negative value of the local pressure, showed three distinct regimes: εxx(0%–5%), εxx(5%–13%) and εxx(13%–30%). The first regime corresponds to the fast nucleation of quasi-defects while the last one showed an inversion in the trend during the stress-softening regime with a moderate decreasing tendency. The three analyses show that the plastic deformation in this amorphous material commences with the nucleation of stress-induced defects without significant changes in the molecular degrees of freedom. Despite the chemical nature and inherent internal structure of the material under study, our findings support Argon et al.’s theory [1–4] as well as that of subsequent investigators [4,5] in that local structural rearrangements exist at locations where particles (beads) forming the material are loosely packed; these regions are termed the local shear transformation zones (STZ).

Slippage and nanorheology of thin liquid polymer films

Thin liquid films on surfaces are part of our everyday life; they serve, e.g., as coatings or lubricants. The stability of a thin layer is governed by interfacial forces, described by the effective interface potential, and has been subject of many studies in recent decades. In recent years, the dynamics of thin liquid films has come into focus since results on the reduction of the glass transition temperature raised new questions on the behavior of especially polymeric liquids in confined geometries. The new focus was fired by theoretical models that proposed significant implication of the boundary condition at the solid/liquid interface on the dynamics of dewetting and the form of a liquid front. Our study reflects these recent developments and adds new experimental data to corroborate the theoretical models. To probe the solid/liquid boundary condition experimentally, different methods are possible, each bearing advantages and disadvantages, which will be discussed. Studying liquid flow on a variety of different substrates entails a view on the direct implications of the substrate. The experimental focus of this study is the variation of the polymer chain length; the results demonstrate that inter-chain entanglements and in particular their density close to the interface, originating from non-bulk conformations, govern the liquid slip of a polymer.

Structure and Dynamics of Ring Polymers: Entanglement Effects Because of Solution Density and Ring Topology

The effects of entanglement in solutions and melts of unknotted ring polymers have been addressed by several theoretical and numerical studies. The system properties have been typically profiled as a function of ring contour length at fixed solution density. Here, we use a different approach to investigate numerically the equilibrium and kinetic properties of solutions of model ring polymers. Specifically, the ring contour length is maintained fixed, while the interplay of inter- and intra-chain entanglement is modulated by varying both solution density (from infinite dilution up to \approx 40 % volume occupancy) and ring topology (by considering unknotted and trefoil-knotted chains). The equilibrium metric properties of rings with either topology are found to be only weakly affected by the increase of solution density. Even at the highest density, the average ring size, shape anisotropy and length of the knotted region differ at most by 40% from those of isolated rings. Conversely, kinetics are strongly affected by the degree of inter-chain entanglement: for both unknots and trefoils the characteristic times of ring size relaxation, reorientation and diffusion change by one order of magnitude across the considered range of concentrations. Yet, significant topology-dependent differences in kinetics are observed only for very dilute solutions (much below the ring overlap threshold). For knotted rings, the slowest kinetic process is found to correspond to the diffusion of the knotted region along the ring backbone.

Confinement Effects on Chain Entanglement in Free-Standing Polystyrene Ultrathin Films

A study of the confinement effects on chain entanglements in free-standing ultrathin (<100 nm) polymer films is presented. Chain entanglements are probed by deter- mining the lifetime and breakup time scale of a branched network of suspended fibers formed from the annealing of these films. Films of polystyrene (between 50 and 100 nm) cast via flow coating are suspended atop lithographically patterned arrays of pillars. The films are then annealed above the glass transition temperature, where holes are randomly formed. The holes expand exponentially due to capillary forces and impinge upon each other to form a suspended, branched network of fibers. The thinning of fibers as well as the lifetime and breakup of this fibernetworkisobservedviaopticalmicroscopy.Amodelfortheviscoelastic-capillarythinningof fiberscanbeappliedtodetermine a time scale for the breakup of individual samples. The decay of this time scale, below a critical parent film thickness, shows a transition between interchain and self-entanglements when crossing into a confined regime, illustrating a significantly decreased interchain entanglement density and breakdown in the entangled network of the polymer melt. This analysis ofconfinement effects on chain entanglement extends the understanding of ongoing studies into suspended fiber formation from the melting of free- standing polymer thin films. A better knowledge of chain entanglements in confined systems will make future fabrication of nanoscale suspended fibers, new architectures, and subsequent devices more controlled and accessible.

Brownian dynamics of a compressed polymer brush model. Off-equilibrium response as a function of surface coverage and compression rate

We study the compressive behaviour of a polymer-covered surface (i.e., a "polymer brush") using Brownian dynamics simulations. The model consists of grafted chains with variable flexibility, variable intra- and inter-chain interactions, as well as different surface coverage. We discuss the polymer brush response to confinement by considering variable rates of compression under a hard plane. Our results show a small degree of inter-chain entanglement, regardless of whether the interaction is attractive or merely excluded volume. We observe that the molecular shape depends strongly on the surface coverage. Dense brushes exhibit a limited degree of lateral deformation under compression; instead, chains undergo a transition that produces a local patch with near-solid packing. This effect due to surface density can be undone partially by increasing the attractive nature of the chain interaction, by modulating the rate of compression, or by allowing "soft anchoring", i.e., the possible Brownian drift of the grafting bead on the surface. We have also studied the polymer brush relaxation while maintaining the compressing plane, as well as after its sudden removal. We find evidence that also the relaxation depends on surface density; dense brushes appear to be configurationally frustrated at high compression and are unable to undergo swelling, regardless of the pressure applied.

Study of structural evolution during controlled degradation of ultrathin polymer films

The structural aspects of polyacrylamide thin films annealed at degradation threshold temperature have been studied as a function of annealing time using in situ X-ray reflectivity technique in vacuum. We observe significant decrease of thickness and increase of density with annealing time for all the films. The dynamical behavior of the changes was modeled in terms of two distinct exponential decay functions, following our earlier observation of two different time scales for the chemical modification pathways, and was found to be in excellent agreement with the data. The diffusion coefficients of the polymer chains corresponding to the two modes are found to be different by an order of magnitude. It was found that the two dynamical modes correspond to the formation of two degradation products at two different rates. The larger time constants for both the modes in case of thickness reduction compare to the chemical changes was explained in terms of inter-chain entanglement and attachment of the polymer with the substrate.

CRYSTALLIZATION BEHAVIOR OF CHAIN-DISENTANGLED POLY(ETHYLENE TEREPHTHALATE)

The chain-disentangled poly ( ethylene terephthalate) ( PET) samples were prepared by freeze-extracting PET solutions (with concentrations ranged from 0. 1 ～ 10 g /dL,in three types of solvent) and were characterized by Fourier transform infrared spectroscopy ( FTIR),wide-angle X-ray diffraction ( WAXD) and differential scanning calorimetry (DSC). WAXD curves showed that,compared with the chain interpenetrated and entangled PET sample quenched from the melt,chain-disentangled PET samples crystallized more easily. By FTIR spectra,it was found that the level of chain disentanglement and crystallinity increased with decreasing solution concentration. But at high dilution,distances between chains became too great to crystallize during the extracting process. For a solution concentration near the overlap concentration c* ,it's advantageous not only to chain disentanglement,but also to the formation of ordered structure and crystallization. Moreover crystallization behavior of PET was affected by solvent used to prepare samples due to the influences of solvent power on the interactions between coils and then the level of chain disentanglement of these samples. When the concentrations of the solutions are lower than the overlap concentration c* ,the PET samples prepared from the good solvent have more orderly structure due to much fewer interchain entanglements. While the concentrations of the solutions are higher than c* ,samples prepared from the bad solvents have more orderly structure. Furthermore,The DSC and WAXD analysis results indicated the samples prepared by freeze-extracting PET solutions were partially crystallized. It's not full disorder in amorphous regions and was a metastable state between order and diorder. After the same annealling,chain-disentangled PET samples were prone to form ordered structure and had a higher crystallinity compared with the chain-entangled PET samples.

Confinement Effects on Chain Dynamics and Local Chain Order in Entangled Polymer Melts

Effects of nanometric confinement on polymer structure and dynamics have been in the focus for more than 15 years, primarily with the aim of providing the physical understanding for nanoscale polymer applications such as in composite materials. Changes in Tg are probably the most researched, but still controversial issue, with clear and intuitively expected indications of slowed-down segmental dynamics for the case of strongly absorbing surfaces but sometimes conflicting trends and a lack of understanding of the physical basis for the often decreased Tg close to free or nonabsorbing interfaces.1−8 One may expect that potential changes in Tg, being related to the time scale of segmental relaxation, should directly influence also larger scale relaxations. However, even slow mechanical relaxation around Tg and aging processes below Tg appear to bear no simple relation to the observed Tg changes,9,10 and the reason may be sought in a modified monomer packing persisting over length scales much beyond the radius of gyration (Rg), as seen in computer simulations.(2) At larger length scales, changes in the whole-chain conformation, as again seen in simulations,2,4 have been assessed by scattering techniques,11−15 with most studies concluding no deviation from Gaussian behavior. Nevertheless, the self-concentration is expected to be increased locally since the random walk of a chain close to a neutral interface is reflected onto itself. Consequently, a reduced interchain entanglement density has been discussed as the reason for enhanced flow of confined chains.15−18 In contrast, a “sticky” surface or local orientation effects and thus anisotropic dynamics of the segments close to an interface are thought to be the reason for enhanced elasticity(19) or reduced diffusion coefficients.20,21 Interestingly, a slowdown of diffusion has also been reported for chains close to a free surface,(22) in apparent contrast to the (sometimes only transiently) reduced viscosity observed by others.15,17,18 Annealing and nonequilibrium effects may thus play an important role.7,18 Note that in all cases the effects were observed in a range up to or even beyond Rg. In this Communication, we present first results on the degree of anisotropy of segmental orientation fluctuations in entangled and geometrically confined chains in two different types of well-defined model nanocomposites with weakly interacting interfaces. We address temperatures far above Tg and time scales beyond the bulk entanglement time τe, providing a molecular-basis view of the discussed phenomena. We use a recently established multiple-quantum (MQ) NMR technique,23−26 which probes the time-dependent degree of local chain orientation via the monomer-averaged apparent residual dipolar coupling constant, Dres. At a given time and temperature, the experimental intensity at short pulse-sequence times τDQ depends on the square of this quantity; more precisely, it is directly proportional to the orientation autocorrelation function where θ is the segmental orientation relative to the external magnetic field. In polymer melts, the decay of C(t) reflects chain motions in the tube-model regimes II−IV,23,26 and its magnitude C(τe)1/2 ∼ 1/Ne reflects the macroscopic elasticity in terms of the number of segments in an entangled strand (tube diameter). In networks, C(t→∞)1/2 ∼ 1/Nc exhibits a long-time plateau that at high cross-link density is directly proportional to the cross-link density.(25)

Strain hardening in bidisperse polymer glasses: Separating the roles of chain orientation and interchain entanglement

The effects of entanglement and chain orientation on strain hardening in glassy polymers are separated by examining mixtures of chains with different lengths. Simulations show that the orientation of a molecule of a given chain length is the same in monodisperse systems and bidisperse mixtures, even when entangled and unentangled chains are mixed. In addition, the stress in mixtures is equal to the weighted average of the stresses in monodisperse systems. These results indicate that chains contribute independently to strain hardening, that chain orientation is determined by local interactions with the surrounding glass, and that entanglements play at most an indirect role in strain hardening in the range of strains typically studied. We discuss these results in the context of recent theories.

Exploring Origins of Interfacial Yielding and Wall Slip in Entangled Linear Melts during Shear or after Shear Cessation

We study yielding at interface between a solid wall and entangled polymer melts. At a average rate higher than the terminal relaxation rate, a combination of rheometric and particle-tracking velocimetric (PTV) measurements reveals apparent wall slip (or interfacial yielding) at a strain γiy, just beyond the stress overshoot. PTV observations show that the interfacial yielding occurs at a higher strain in the presence of a faster rate of shear. Shear cessation at a strain lower than γiy is observed to also result in interfacial failure, suggesting that the finite adhesion can be overcome in quiescence by the residual elastic retraction force. These two kinds of interfacial failure can be theoretically understood in terms of the intrachain elastic retraction forces overcoming the melt adhesion arising from interchain entanglement interactions between adsorbed and bulk chains.

Multistep relaxation in equilibrium polymer solutions: A minimal model of relaxation in “complex” fluids

We examine the rheological and dielectric properties of solutions of equilibrium self-assembling particles and molecules that form polydisperse chains whose average length depends on temperature and concentration (free association model). Relaxation of the self-assembling clusters proceeds by motions associated either with cluster rotations, with diffusive internal chain dynamics, or with interchain entanglement interactions. A hierarchy of models is used to emphasize different physical effects: Unentangled rodlike clusters, unentangled flexible polymers, and entangled chains. All models yield a multistep relaxation for low polymer scission rates ("persistent polymers"). The short time relaxation is nearly exponential and is dominated by the monomeric species and solvent, and the long time relaxation is approximately a stretched exponential, exp[-(t/tau)(beta)], a behavior that arises from an averaging over the equilibrium chain length distribution and the internal relaxation modes of the assembled structures. Relaxation functions indicate a bifurcation of the relaxation function into fast and slow contributions upon passing through the polymerization transition. The apparent activation energy for the long time relaxation becomes temperature dependent, while the fast monomeric relaxation process remains Arrhenius. The effective exponent beta(T), describing the long time relaxation process, varies monotonically from near unity above the polymerization temperature to a low temperature limit, beta approximately 13, when the self-assembly process is complete. The variation in the relaxation function with temperature is represented as a function of molecular parameters, such as the average chain length, friction coefficient, solvent viscosity, and the reaction rates for particle association and dissociation.

Rheological properties of novel thermo-responsive polycarbonates aqueous solutions

Thermo-responsive multiblock polycarbonates were facilely synthesized by covalently binding poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) blocks, using triphosgene as coupling agent and pyridine as catalyst. The aqueous solutions of thermo-responsive polycarbonates were investigated by rheological measurements. Steady-state shear measurements reveal that the polycarbonate solutions exhibit shear-thinning behavior and the hydrophilic content has a pronounced effect on the flow behavior of the polycarbonates aqueous solutions. The shear viscosity decreases with increasing poly(ethylene oxide) (PEO) composition. The increase of viscosity with increasing concentration is probably attributed to the formation of stronger network owing to interchain entanglement of PEO block at higher concentration. When the flow curves are fitted to the power law model, flow index is obtained to be less than 1, as exhibiting typical pesudoplastic fluid. The viscoelastic properties of the system also show close dependence on the composition of polycarbonates. Temperature sweep confirms that the multiblock polycarbonates exhibit thermo-responsive properties. For 7% aqueous solution of polycarbonate with composition ratio of EO to PO of 1/1, the sol-gel transition occurs at 37 °C, which makes the system suitable as an injectable drug delivery system.

Comparative Study of Temperature-Induced Association of Cyclic and Linear Poly(N-isopropylacrylamide) Chains in Dilute Solutions by Laser Light Scattering and Stopped-Flow Temperature Jump

We have comparatively studied the association of cyclic- and linear-poly(N-isopropylacrylamide) (c-PNIPAM and l-PNIPAM) chains with varying chain lengths and end groups in dilute aqueous solutions by laser light scattering (LLS) and stopped-flow temperature-jump measurements. Dynamic and static LLS results reveal that the heating leads to a microphase transition. The resultant structures of interchain aggregates depend on the heating rate and the chain topologies. In comparison with l-PNIPAM chains, a slow heating of c-PNIPAM chains in the solution results in stable mesoglobules with a lower average aggregation number, a looser structure, and a smaller average size (∼290 nm). The temperature-jump-induced association of c-PNIPAM chains in the stopped-flow measurement reveals two kinetic growth stages, which were tentatively ascribed to the loose packing of contracted c-PNIPAM chains and further contraction-induced fragmentation of initially packed c-PNIPAM chains due to the lack of interchain entanglements. On the other hand, for l-PNIPAM chains, the intrachain contraction and interchain penetration/entanglement simultaneously occur as the temperature increases, leading to larger and more compact aggregates whose size increases with the solution temperature.

Conformation of Single Poly(methyl methacrylate) Chains in an Ultra-Thin Film Studied by Scanning Near-Field Optical Microscopy

The conformation of a single poly(methyl methacrylate) (PMMA) chain was studied by scanning near-field optical microscopy (SNOM). Here we discuss the conformation of PMMA in the confined geometry of the thin film with a thickness less than the unperturbed chain dimension in the bulk state. The direct observation by SNOM was performed for individual fluorescence-labeled PMMA chains dispersed in the thin films of the unlabeled PMMA prepared by the spin coating and Langmuir-Blodgett techniques. We examined the effect of the constraint in the height direction on the radius of gyration in the direction parallel to the film surface, Rxy, i.e., the chain dimension normal to the confinement. In the thickness range of 1–100 nm, Rxy in an ultra-thin film was not significantly altered from that in the bulk state, indicating that the PMMA chain has lowered interchain entanglement in the ultra-thin film.

Effect of the Physicochemical Properties of Poly(Ethylene Glycol) Brushes on their Binding to Cells

We investigated the effect of the number of oxyethylene groups (polymer molecular weight) and the interchain binding and/or entanglements of methoxy-terminated-poly(ethylene glycol) (m-PEG) brushes on their ability to adsorb to living malignant melanoma B16F10 cells. We used the atomic force microscope colloid probe method to determine the adhering ability of the m-PEG brushes to the cells, as the magnitude of the adhesion force between the m-PEG modified particles and the living cells in a physiological buffer was related to the binding strength of the m-PEGs to the cells. We saw that m-PEG brushes (average molecular weights 330, 1900, and 5000 g/mol), which were chemically attached to silica particles, may bind to living B16F10 cells. The binding of m-PEGs to living B16F10 cells increased as the oxyethylene chain length of the m-PEGs increased, if the m-PEGs had a low degree of entanglements or little inter-m-PEG chain binding. A high degree of entanglements or interchain binding decreased the ability of an m-PEG chain to bind to a living cell. The effect of m-PEG (molecular weight 1900 g/mol) being present at cell surfaces for 24 h was also seen not to induce the death of the cells or affect their growth.

Self-Associating Block Copolymer Networks for Microchip Electrophoresis Provide Enhanced DNA Separation via “Inchworm” Chain Dynamics

We describe a novel class of DNA separation media for microchip electrophoresis, "physically cross-linked" block copolymer networks, which provide rapid (<4.5 min) and remarkably enhanced resolution of DNA in a size range critical for genotyping. Linear poly(acrylamide-co-dihexylacrylamide) (LPA-co-DHA) comprising as little as 0.13 mol % dihexylacrylamide yields substantially improved electrophoretic DNA separations compared to matched molar mass linear polyacrylamide. Single-molecule videomicroscopic images of DNA electrophoresis reveal novel chain dynamics in LPA-co-DHA matrixes, resembling inchworm movement, to which we attribute the increased DNA resolution. Substantial improvements in DNA peak separation are obtained, in particular, in LPA-co-DHA solutions at polymer/copolymer concentrations near the interchain entanglement threshold. Higher polymer concentrations yield enhanced separations only for small DNA molecules (<120 base pairs). Hydrophobically cross-linked networks offer advantages over conventional linear polymers based on enhanced separation performance (or speed) and over chemically cross-linked gels because hydrophobic cross-links can be reversibly broken, allowing facile microchannel loading.

INFLUENCE OF SOLVENT UPON THE FORMATION OF ORDERED STRUCTURE IN PARTIALLY DISENTANGLED POLY(VINYL CHLORIDE)

The partially disentangled polymer samples prepared are expected to crystallize easier than bulk polymers,which can be attributed to much fewer interchain entanglements within and between particles.Poly(vinyl chloride) (PVC) samples were prepared by freeze-extracting the solutions in various solvents and with varying concentrations.The results of FTIR analysis showed that when the concentrations of the solutions were lower than the overlap concentration c*,the PVC samples prepared from the good solvent had more ordered structure due to much fewer interchain entanglements.While the concentrations of the solutions were higher than c*,the PVC samples prepared from the bad solvents had more ordered structure.

Influence of entanglements on glass transition of atactic polystyrene

AbstractFreeze‐dried samples were prepared from dilute solutions of atactic polystyrene (a‐Ps) in benzene in a concentration range of 1 × 10−1 to 2 × 10−5 g/mL, and their glass transition temperatures (Tg) were determined by differential scanning calorimetry. It was found that below a critical concentration (C), the Tg of samples decreases linearly with decreasing logarithmic concentration of solutions. The freeze‐dried samples were annealed at a constant temperature for various times or at various temperatures for the same period of time. The Tg of samples prepared from solutions of concentration below C was observed to shift to higher temperature with increasing annealing temperature or annealing time, finally approaching that of the bulk sample. Fourier transform infrared (FTIR) spectra of the freeze‐dried samples were determined and were compared with the bulk sample. Significant changes in line width and absorption intensity were observed in the spectra of the freeze‐dried samples, indicating that the packing of segments is in a more dilatant state. During annealing, the packing of segments in the samples gradually approaches that of the bulk sample, diminishing the differences in FTIR spectra between the freeze‐dried sample and the bulk sample. The experimental observations are discussed, and it is assumed that intrachain and interchain entanglements may play an important role in glass transition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2243–2251, 2005

Discrete film thickness in polyacrylamide-CdS nanocomposite ultrathin films

A nanocomposite of polyacrylamide, a water soluble polymer, and nanocrystalline CdS has been prepared using a chemical route. Transmission electron microscope observation shows that the particles are attached via the polymer coils. The reduction of viscosity for the composite, despite the increase in concentration, indicates a reduction of interchain entanglement between the composite coils. Ultrathin films were prepared from the nanocomposite and pure polyacrylamide using spin coating on a Si(100) substrate in the speed range of 500 to 5000 rpm. X-ray reflectivity studies of the pure polymer and composite films were carried out in vacuum. The thickness of the composite films varies nonmonotonically with spinning speed and is found to lie in discrete "bands" of thickness separated by "forbidden regions." The power law behavior of the thickness with the spinning speed was also found to be different for the composite films in comparison to the polymer ones. A model has been proposed in terms of discrete numbers of layers composed of CdS-attached polymer coils to explain the phenomena.

Sparsely cross-linked "nanogel" matrixes as fluid, mechanically stabilized polymer networks for high-throughput microchannel DNA sequencing.

We have developed sparsely cross-linked "nanogels", subcolloidal polymer structures composed of covalently linked, linear polyacrylamide chains, as novel replaceable DNA sequencing matrixes for capillary and microchip electrophoresis. Nanogels were synthesized via inverse emulsion (water-in-oil) copolymerization of acrylamide and a low percentage (approximately 10(-4) mol %) of N,N-methylene bisacrylamide (Bis). Nanogels and nanogel networks were characterized by multiangle laser light scattering and rheometry, respectively, and tested for DNA sequencing in both capillaries and chips with four-color LIF detection. Typical nanogels have an average radius of approximately 230 nm, with approximately 75% of chains incorporating a Bis cross-linker. The properties and performance of nanogel matrixes are compared here to those of a linear polyacrylamide (LPA) network, matched for both polymer weight-average molar mass (M(w)) and the extent of interchain entanglements (c/c). At sequencing concentrations, the two matrixes have similar flow characteristics, important for capillary and microchip loading. However, because of the physical network stability provided by the internally cross-linked structure of the nanogels, substantially longer average read lengths are obtained under standard conditions with the nanogel matrix at a 98.5% accuracy of base-calling (for CE: 680 bases, an 18.7% improvement over LPA, with the best reads as long as 726 bases, compared to 568 bases for the LPA matrix). We further investigated the use of the nanogel matrixes in a high-throughput microfabricated DNA sequencing device consists of 96 separation channels densely fabricated on a 6-in. glass wafer. Again, preliminary DNA sequencing results show that the nanogel matrixes are capable of delivering significantly longer average read length, compared to an LPA matrix of comparable properties. Moreover, nanogel matrixes require 30% less polymer per unit volume than LPA. The addition of a small amount of low molar mass LPA or ultrahigh molar mass LPA to the optimized nanogel sequencing matrix further improves read length as well as the reproducibility of read length (RSD < 1.6%). This is the first report of a replaceable DNA sequencing matrix that provides better performance than LPA, in a side-by-side comparison of polymer matrixes appropriately matched for molar mass and the extent of interchain entanglements. These results could have significant implications for the improvement of microchip-based DNA sequencing technology.