Dimensions Of Macromolecules Research Articles

Polymer-Tethered Nanoparticles: From Surface Engineering to Directional Self-Assembly.

Current interest in nanoparticle ensembles is motivated by their collective synergetic properties that are distinct from or better than those of individual nanoparticles and their bulk counterparts. These new advanced optical, electronic, magnetic, and catalytic properties can find applications in advanced nanomaterials and functional devices, if control is achieved over nanoparticle organization. Self-assembly offers a cost-efficient approach to produce ensembles of nanoparticles with well-defined and predictable structures. Nanoparticles functionalized with polymer molecules are promising building blocks for self-assembled nanostructures, due to the comparable dimensions of macromolecules and nanoparticles, the ability to synthesize polymers with various compositions, degrees of polymerization, and structures, and the ability of polymers to self-assemble in their own right. Moreover, polymer ligands can endow additional functionalities to nanoparticle assemblies, thus broadening the range of their applications.In this Account, we describe recent progress of our research groups in the development of new strategies for the self-assembly of nanoparticles tethered to macromolecules. At the beginning of our journey, we developed a new approach to patchy nanoparticles and their self-assembly. In a thermodynamically driven strategy, we used poor solvency conditions to induce homopolymer surface segregation in pinned micelles (patches). Patchy nanoparticles underwent self-assembly in a well-defined and controlled manner. Following this work, we overcame the limitation of low yield of the generation of patchy nanoparticles, by using block copolymer ligands. For block copolymer-capped nanoparticles, patch formation and self-assembly were "staged" by using distinct stimuli for each process. We expanded this work to the generation of patchy nanoparticles via dynamic exchange of block copolymer molecules between the nanoparticle surface and micelles in the solution. The scope of our work was further extended to a series of strategies that utilized the change in the configuration of block copolymer ligands during nanoparticle interactions. To this end, we explored the amphiphilicity of block copolymer-tethered nanoparticles and complementary interactions between reactive block copolymer ligands. Both approaches enabled exquisite control over directional and self-limiting self-assembly of complex hierarchical nanostructures. Next, we focused on the self-assembly of chiral nanostructures. To enable this goal, we attached chiral molecules to the surface of nanoparticles and organized these hybrid building blocks in ensembles with excellent chiroptical properties. In summary, our work enables surface engineering of polymer-capped nanoparticles and their controllable and predictable self-assembly. Future research in the field of nanoparticle self-assembly will include the development of effective characterization techniques, the synthesis of new functional polymers, and the development of environmentally responsive self-assembly of polymer-capped nanoparticles for the fabrication of nanomaterials with tailored functionalities.

Small-Angle Scattering as a Structural Probe for Nucleic Acid Nanoparticles (NANPs) in a Dynamic Solution Environment.

Nucleic acid-based technologies are an emerging research focus area for pharmacological and biological studies because they are biocompatible and can be designed to produce a variety of scaffolds at the nanometer scale. The use of nucleic acids (ribonucleic acid (RNA) and/or deoxyribonucleic acid (DNA)) as building materials in programming the assemblies and their further functionalization has recently established a new exciting field of RNA and DNA nanotechnology, which have both already produced a variety of different functional nanostructures and nanodevices. It is evident that the resultant architectures require detailed structural and functional characterization and that a variety of technical approaches must be employed to promote the development of the emerging fields. Small-angle X-ray and neutron scattering (SAS) are structural characterization techniques that are well placed to determine the conformation of nucleic acid nanoparticles (NANPs) under varying solution conditions, thus allowing for the optimization of their design. SAS experiments provide information on the overall shapes and particle dimensions of macromolecules and are ideal for following conformational changes of the molecular ensemble as it behaves in solution. In addition, the inherent differences in the neutron scattering of nucleic acids, lipids, and proteins, as well as the different neutron scattering properties of the isotopes of hydrogen, combined with the ability to uniformly label biological macromolecules with deuterium, allow one to characterize the conformations and relative dispositions of the individual components within an assembly of biomolecules. This article will review the application of SAS methods and provide a summary of their successful utilization in the emerging field of NANP technology to date, as well as share our vision on its use in complementing a broad suite of structural characterization tools with some simulated results that have never been shared before.

A study of the viscosity of phenol–formaldehyde resin modified with furfural–acetone monomer FA

The results of an evaluation of the relative and dynamic viscosities of phenol–formaldehyde resin modified with furfural–acetone monomer FA monomer are presented. That there is increasing viscosity of the modified adhesive composition is established due to the formation of polycomplexes, these being new supramolecular structures with increased dimensions of macromolecules of higher molecular mass.

Investigation of Removal Possibilities of Colloidal Alumina from Aqueous Solution by the Use of Anionic Polyacrylamide

Purification of drinking and industrial water required usage of high molecular weight polymer to cause flocculation process of dispersed suspension of contaminants. Polyelectrolytes, including ionic polyacrylamide are especially appropriate for these purposes, because in this case the suspension stability can be controlled by both steric and electrostatic forces. Thus the influence of solution pH and hydrolysis degree (carboxyl groups content) of anionic polyacrylamide (PAM) on the alumina (Al2O3) suspension stability were studied. The turbidimetry was applied for determination of the examined systems stability. The mechanism of suspension stabilization or destabilization in the polymer presence was proposed on the basis of determined parameters: adsorbed amount of PAM, its adsorption layer thickness, linear dimensions of macromolecules in the solution and zeta potential of alumina particles covered with the polyacrylamide layer. The greatest decrease of the alumina suspension stability in the polymer presence in comparison to that without the polymer was obtained at pH 6 after the addition of PAMs with higher molecular weight (i.e. 14 000 0000) and hydrolysis degrees 20 and 30% (efficient neutralization of solid surface charge). In turn, the most unstable alumina system proved to be that prepared at pH 9 containing PAM with the highest molecular weight and the greatest hydrolysis degree (causing the most effective bridging flocculation).

Impact of polyacrylamide with different contents of carboxyl groups on the chromium (III) oxide adsorption properties in aqueous solution

The main goal of experiments was determination of solution pH and contents of anionic groups in polyacrylamide (PAM) macromolecules on the stability mechanism of chromium (III) oxide suspension. The spectrophotometry, potentiometric titration, microelectrophoresis, viscosimetry and turbidimetry were applied. They enabled determination of polymer adsorbed amount, surface and diffusion charges of solid particles with and without PAM, thickness of polymer adsorption layer, macromolecule dimensions in the solution and stability of the Cr2O3 – polymer systems, respectively. It was found that adsorption of anionic PAM decreases and thickness of polymeric adsorption layer increases with the increasing pH. Slightly higher adsorption was obtained for the PAM samples containing a greater number of carboxyl groups. At pH 3 and 9 insignificant deterioration of stability conditions of Cr2O3 particle covered with polyacrylamide was observed (neutralization of solid positive charge by the adsorbed polymeric chains (pH 3) and single polymeric bridges formation (pH 9)). The electrosteric repulsion between the solid particles covered with PAM layers at pH 6, is the main reason for significant improvement of Cr2O3 suspension stability in the polymer presence.

Temperature dependence of the intrinsic viscosity of poly(methyl methacrylate) in binary solvents used as eluents for liquid chromatography under critical conditions

The effect of temperature on the values of the intrinsic viscosity and swelling degree of poly(methyl methacrylate) macromolecular coils in binary solvents used as eluents for liquid chromatography under critical conditions is studied. It is shown that these values are little temperature-dependent. This circumstance makes it possible to assume that the temperature dependences of retention characteristics are minimally contributed by changes in the dimensions of macromolecules in poly(methyl methacrylate) solutions.

Viscosity of dilute solutions of styrene copolymers in the course of polymer-analogous transformations

The properties of dilute solutions of styrene copolymers and their porphyrin derivatives prepared via the functional group transformations have been studied in DMF at 20–35°C. The effect of the copolymer composition, on the intrinsic viscosity, the Huggins constant, the macromolecule dimensions, and thus on the interaction with solvent has been elucidated. The nature and content of functional groups in the polymer influence the behavior of macromolecule coil in the solution. Introduction of the porphyrin fragment loosens the macromolecular coil, but does not qualitatively change the solution behavior.

Structural and conformational properties of hyperbranched copolymers based on perfluorinated germanium hydrides

Two series of hyperbranched copolymers based on perfluorinated germanium hydrides of various topological structures are studied in dilute chloroform solutions by the methods of molecular hydrodynamics and optics. The first series is composed of copolymers with various molecular masses (from 2.3 × 104 to 31 × 104) that contain rigid linear chains between branching points and various amounts of branching points in cascades of the dendritic fragment, while the second series is comprised of copolymers that, at close branching degrees, on average, are characterized by a looser structure owing to a large amount of linear units at the periphery of macromolecules with M = (2.5 × 104)−(23 × 104). Macromolecules of the studied polymers have compact dimensions and a high density of the polymer substance; their shape asymmetry is low. In terms of these characteristics, they approach dendrimers. At a fixed molecular mass, the copolymers with a loose structure have higher dimensions of macromolecules and higher intrinsic viscosities.

Self-organization of macromolecules and liquid-crystalline phase transitions in solutions of cellulose esters

For hydroxypropyl cellulose-ethanol, hydroxyethyl cellulose-water, and cyanoethyl cellulose-DMAA systems, phase diagrams are constructed and the regions of existence of isotropic and anisotropic phases and the dimensions of macromolecules and supramacromolecular particles in a wide composition range are determined through the use of the cloud-point method, polarization microscopy, the turbidityspectrum method, dynamic light-scattering measurements, and a polarization optical apparatus. It is shown that the formation of LC phases with an increase in the polymer concentration is associated with a significant enlargement of supramolecular particles.

Free energy and dimensions of macromolecules under confinement in layered assemblies

AbstractThe changes in the free energy ΔA accompanying penetration of polymer solutions from bulk into slit‐like cavities were determined by lattice simulations. In dilute solutions the thermodynamics of penetration is controlled mainly by the parameter ϵw specifying interaction between polymer and walls of repulsive or adsorptive cavities. However, the magnitude of |ΔA| is substantially reduced by increasing concentration ∅︁ in bulk solution. Furthermore, compression of chains by concentration in good solvents and adsorptive cavities was found to be larger in the slit then in the bulk. At intermediate confinement, a region of a minimum coil size was observed at all concentrations and attraction strengths, where molecules are squeezed along all three axes.

Universal behavior of polymers in blends, solutions, and supercritical mixtures and implications for the validity of the random phase approximation

Blending (or mixing) of macromolecules is widely used to tailor the properties of polymeric materials and small-angle neutron scattering (SANS) has provided detailed information at the molecular level on the ability of different polymer species to mix or segregate at various thermodynamic conditions. For two decades, SANS data have been analyzed via the de Gennes “random phase approximation” (RPA) [P.-G. de Gennes, Scaling Concepts in Polymer Physics, second ed., Cornell University Press, Ithaca, London, 1979], which is based on the assumption that the dimensions of polymer chains remain unchanged on mixing for all concentrations and temperatures. Here we investigate the effect of temperature and concentration on the dimensions of macromolecules in blends using SANS and high-concentration labeling methods and construct a generic phase diagram, which specifies the range of validity of the RPA. Using scaling arguments, we demonstrate a parallel between the structure–property relationships in blends and solutions of polymers in small molecule solvents and reveal the impact of the chain length of the polymeric solvent on the phase behavior of polymer blends. The results offer new insights into the universality of the thermodynamic properties and structure of macromolecules in polymeric, liquid and supercritical solvents.

Determining Protein Size Using an Electrochemically Machined Pore Gradient in Silicon

Porous silicon films displaying a distribution of pore dimensions can be generated by electrochemically etching silicon in aqueous ethanolic HF using an asymmetric electrode configuration. The median pore size and breadth of the size-distribution in the film can be set by adjusting the HF concentration, current density, and position of the counter electrode relative to the silicon electrode. Films with pore sizes in the range of a few nanometers are used as size-exclusion matrices to perform an on-chip determination of macromolecule dimensions. The test molecule used in this study is bovine serum albumin (BSA). Optical reflectivity spectra of the thin porous Si films display distinctive shifts in the Fabry–Perot fringes in regions of the film where the pore dimensions are larger than a critical size, interpreted to be the characteristic dimensions of the protein. Gating of the protein in and out of the porous films is demonstrated by adjustment of the solution pH below and above the pI (isoelectric point) value, respectively.

Fibrillar polysaccharides in marine macromolecular organic matter as imaged by atomic force microscopy and transmission electron microscopy

A consensus is now emerging that the structure of organic macromolecules will determine their function in aquatic systems. Transmission electron microscopy (TEM) is a widely used technique to study the morphology of biomolecules that, under the proper conditions, allows for accurate determination of the shapes and horizontal dimensions of macromolecules. Atomic force microscopy (AFM) is a newe: technique that has better overall resolution, particularly on the vertical scale. Although careful controls must be in place for both techniques to avoid the introduction of artifacts, they are highly complementary techniques for the study of natural colloids and can, when used together, reveal complementary information about the relative abundance and structures of aquatic macromolecules and colloids. Although AFM techniques have not previously been applied to the study of oceanic macromolecules and colloids, TEM has been used, albeit often under nonoptimal staining and embedding conditions. In this study, colloid samples from the Gulf of Mexico and Middle Atlantic Bight of nominal sizes 1–200 nm were collected by cross-flow ultrafiltration, diafiltered, and freeze-dried. Rehydrated colloids were analyzed in parallel by AFM and TEM using standardized techniques. Results from estuarine-, surface-, and deep-water samples show that an important fraction of colloidal organic matter (COM) consists of fibrillar material, which is rich in polysaccharides and “fresher” (i.e., has a younger radiocarbon age) than the bulk COM. This result is important because COM makes up 30–70% of oceanic and estuarine nominally “dissolved” organic matter. Other microparticles appear to be quasi-spherical, often attached to the fibrils like pearls. In the surface waters of the Gulf of Mexico, Middle Atlantic Bight, and Trinity River, fibrils with diameters of l–3 nm and lengths of 100–2,000 nm were predominant. Although fibrils were also observed in samples from the benthic nepheloid layer in the Gulf of Mexico (1,600 m) and Middle Atlantic Bight (2,600 m), a much greater heterogeneity of colloid and macromolecule shapes and sizes was observed in these deeper waters.

Modelling of θ‐conditions for bisphenol—A polycarbonate single chains

AbstractAssessing conformational dimensions of macromolecules is a topic of long‐standing interest. Because of its simplicity, it is attractive to investigate the chain properties in θ‐conditions. Under these special conditions, the effects of excluded volume of the segments of the polymer chain vanish. The molecular chain is only subject to local constraints resulting from the bond structure and the hindrance to rotations about bonds. To model θ‐conditions a contour length dependent cutoff is introduced ensuring that only nonbonded interactions of atoms of neighbouring monomeric units are taken into account for energy calculations. Using this energy model we will show that it is possible to model θ‐conditions of a single bisphenol‐A polycarbonate (BPA‐PC) chain in vacuum by two different methods: (i) (Pseudo‐) Langevin dynamics simulations and (ii) regular reassignment of randomly generated atom velocities during a molecular dynamics simulation. Both methods can be used to avoid oscillative dynamic behaviour of the chain. Calculations of the end‐to‐end vector and the radius of gyration of the equilibrium ensembles derived from simulations at different temperatures show good agreement with experimental data. Thus our model techniques are well suited to simulate θ‐conditions with small computational expense.

A New Scaling Theory of Semiflexible Polymer Phases Near Attracting Surfaces

The finite chain backbone stiffness in polymers gives rise to a number of novel behaviors described on short length scales. We analyze the semiflexible polymer phases near surfaces using a new scaling theory, incorporating the surface attraction in terms of its range and depth. It is found that the phase diagram includes five different phases: desorbed, weakly- adsorbed with both isotropic and nematic-type distribution of polymer segments inside the potential well, strongly-adsorbed states with the isotropic and nematic-type distribution. We draw conclusions on the orders of the transitions between the phases. The stiffness of polymer chain backbone means the presence of an orientation memory be- tween segments along the chain. A rigid rod is the very stiff polymer, for which the persistence length is much larger than the total contour length. This polymer can not be crumpled without breakage. On the other hand a very flexible chain can be crumpled practically on any length scales. It can be crumpled as a whole (as in so-called globule-to-coil transition iii and in the ideal limit it can be crumpled on smaller and smaller length scales (down to the microscopic scales of chain diameter order), carrying a self-similar or fractal structure. For the intermediate cases of semiflexible chain, which are probably the most interesting for applications including biophysical problems, the persistence length is much smaller than the total polymer contour length, so it can be crumpled as a whole in a similar way as a flexible chain. In general, we can treat a semiflexible polymer chain as a flexible one, when we are interested in the universal macroscopic polymer properties measured over the scales of whole macromolecule dimensions. But on the scales smaller than the persistence length the semiflexible structure can be con- sidered as an array of rigid rods interconnected at a fixed angle. (Naturally, the semiflexible wormlike chain can be viewed as the continuous limit of the discrete model iii.) Therefore, on these scales already, semiflexible polymer can not be crumpled without breakage and its properties are essentially different from those of flexible polymer. A wide class of synthetic and

The effect of polymer solution composition and film-forming procedure on aromatic polyamide membrane skin layer structure

Linear polymer phase inversion membrane casting solutions are composed of suspensions of relatively spherical polymer macromolecules. Estimates of macromolecule dimensions can be calculated, dependent on the type and concentration of the components in each particular solution. Membrane skin layer formation may be considered as interpenetration or partial coalescence and subsequent crystallization of solution surface macromolecules. The surface morphology of asymmetric membranes can be characterized by assuming a porous structure. With knowledge of the surface porous structure, membrane performance can be predicted for most solute—solvent combinations and operating conditions. It is assumed that all permeate transport through a membrane skin layer occurs between surface paracrystalline macromolecules. Macromolecule to pore radius comparisons can then be used to determine the effect of the casting composition and/or membrane-making procedure on the disposition and subsequent degree of interpenetration of surface macromolecules. Relationships between the casting composition/membrane-making procedure and interstitial coagulation may be used for membrane design considerations. This method of analysis is shown to be useful in examining reverse osmosis (RO) and ultrafiltration (UF) aromatic polyamide films.

The effect of additives, solvent type, and polymer concentration on macromolecule dimensions

AbstractAn equation is derived to estimate the hydrodynamic volume occupied by a typical linear polymer molecule, knowing only the polymer molecular weight and concentration of polymer in the solution. This equation may be applied to solutions above a minimum polymer concentration. Accuracy of the equation is determined by comparing it to an established method of calculating macromolecule dimensions.Above dilute solution conditions, the volume pervaded by a macromolecule is affected mainly by the polymer molecular weight and concentration of polymer in the solution. Chain dimensions are generally unaffected by the type of polymer, solvent, or additive in the solution.

Intrinsic viscosity and flow birefringence of some comb-like polymers having mesogenic side groups as a function of temperature

The intrinsic viscosity [η] and the flow birefringence of two comb-like polymers as a function of temperature are studied in various solvents. In solvents in which the macromolecule dimensions are smaller the change in [η] is indicated by the positive temperature coefficient and vice versa. The change in macromolecule dimensions with temperature is reflected in the change in flow birefringence.

Universality of coil-globule transition characteristics in two-dimensional lattice models of macromolecules

Coil-globule transitions for various lattice models of macromolecules on a plane are studied by the Monte Carlo method. The universality of its characteristics, especially of the tricritical index ν t = 0·58 ± 0·01 and the cross-over index (parameter) φ=0·6 ± 0·1 and the scaling dependence of the macromolecule dimensions on the degree of polymerization and the temperature are demonstrated. The free energy is studied as a function of the degree of polymerization and the temperature. Chain dimension data are compared with analytical formulae obtained on the basis of mean field theory.

Solvent modified unperturbed dimensions of macromolecules ‐ their determination via NMR ‐ data and their relevance ‐

AbstractTemperature dependent unperturbed and solvent modified unperturbed dimensions of macromolecules are derived, in a first order approximation, from NMR‐data determined on low‐molecular‐weight analogs in the respective milieu. Because the long range interactions ‐ excluded volume and polymer ‐ polymer interaction ‐ are absent in the conformational balance of those models, the macrodimensions derived in this way are the unperturbed ones, with and without the influence of specific solvent action. Studies on head‐to‐head vinyl polymers are reported. It is demonstrated that the unperturbed dimensions in virtually non‐interacting solvents,<r2>o, may exceed those in thermodynamically good ones, <r2>s, as a consequence of differing conformational balance at segmental level.It is pointed out that those temperature and solvent dependent unperturbed dimensions are effective also in polymer solutions, as long as the molecular weight of the polymer is not exceeding the critical length necessary for occurrence of long range interactions.Capabilities in analyzing the conformational balance in plasticized systems and in compatible polymer blends are discussed. Here the conformation of the second component may be studied in parallel, as a consequence of similar concentrations of both partners in the system.θ‐dimensions depend on the type of the pseudoideal solvent. This effect is discussed on the base of NMR studies on the unperturbed conformations at segmental level in the respective θ‐ milieu.