Self‐assembled nanostructures: preparation,characterization, thermal,optical and morphological characteristics of amphiphilic diblock copolymers based on poly(2‐hydroxyethyl methacrylate‐block‐N‐phenylmaleimide)

A series of well‐defined amphiphilic poly[(2‐hydroxyethyl methacrylate)‐block‐(N‐phenylmaleimide)] diblock copolymers containing hydrophilic and hydrophobic blocks of different lengths were synthesized by atom transfer radical polymerization. The properties of the diblock copolymers and their ability to form large compound spherical micelles are described. Their optical, morphological and thermal properties and self‐assembled structure were also investigated. The chemical structure and composition of these copolymers have been characterized by elemental analysis, Fourier transform infrared, ¹H NMR, UV–visible and fluorescence spectroscopy, and size exclusion chromatography. Furthermore, the self‐assembly behavior of these copolymers was investigated by transmission electron microscopy and dynamic light scattering, which indicated that the amphiphilic diblock copolymer can self‐assemble into micelles, depending on the length of both blocks in the copolymers. These diblock copolymers gave rise to a variety of microstructures, from spherical micelles, hexagonal cylinders to lamellar phases. © 2013 Society of Chemical Industry     

Self‐assembled structures in blends of disordered and lamellar block copolymers: SAXS,SANS and TEM study

BACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self‐assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS‐block‐dPMMA)₁/(dPS‐block‐PMMA)₂, were investigated using small‐angle X‐ray scattering, small‐angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature. RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution‐cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with M_n by D ～ M_n^2/3 as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene‐block‐polyisoprene copolymers). CONCLUSIONS: The criterion for forming a single‐domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self‐assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene‐block‐polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. Copyright © 2008 Society of Chemical Industry     

Self‐assembled structures in d8‐polystyrene‐block‐polyisoprene/polystyrene blends in the weak segregation regime: SAXS and TEM study

BACKGROUND: This paper reports an investigation of the microphase‐separated morphology and phase behaviour in blends of d‐polystyrene‐block‐polyisoprene with homopolystyrene in the weak segregation regime, using small‐angle X‐ray scattering and transmission electron microscopy, as a function of composition, weight‐average molecular weight and temperature. The chain length ratio parameter r_M = M_H/M_C (where M_H and M_C are the weight‐average molecular weights of the homopolymer and corresponding block copolymer chain) was selected to encompass all possible types of mutual homopolymer/block copolymer sizes. RESULTS: In the weak segregation regime the polystyrene block chains behave as a ‘wet brush’ for r_M < 1 similarly to the intermediate and strong segregation regimes. For r_M > 1 a macroscopic phase separation occurs. The domain spacing D increases systematically in the range 0 < r_M ≤ 1 with increasing concentration of homopolymer w_P and increasing r_M regardless of the implemented specific morphology, but the slope of the periodicity D versus w_P relation is smaller than in the intermediate and strong segregation regimes. CONCLUSION: The criterion for ‘wet and dry brush’ morphologies has been applied to explain the changes in microdomain morphology during the self‐assembly process. It has been shown that the parameters r_M and χ^3/2N (where χ is the Flory–Huggins parameter and N the number of segments per chain) characterize the slope of the D versus w_P relation in the weak and intermediate segregation regimes. Copyright © 2009 Society of Chemical Industry     

Self‐assembled structures in polystyrene‐block‐polyisoprene‐blend‐polystyrene and polystyrene‐block‐poly(methyl methacrylate)‐blend‐polystyrene or ‐blend‐poly(methyl methacrylate) in the strong segregation regime

This study deals with the investigation of microphase‐separated morphology and phase behaviour in blends of polystyrene‐block‐polyisoprene with homopolystyrene and blends of polystyrene‐block‐poly(methyl methacrylate) with homopoly(methyl methacrylate) or homopolystyrene in the strong segregation regime using small‐angle X‐ray scattering and transmission electron microscopy as a function of composition, molecular weight of homopolymers, r_M and temperature. Parameter r_M = M_H/M_C (where M_H is the molecular weight of homopolymer and M_C that of the corresponding block copolymer) was selected to encompass behaviour of the chains denoted as a ‘wet brush’ (i.e. r_M < 1). The relative domain spacing D/D_o increases in the regime 0 < r_M?1 with increasing concentration of homopolymer w_P and increasing r_M but depends on the specific implemented morphology. We tested a new approximate D/D_o versus w_P relation in the strong segregation regime using block copolymers of high molecular weights. It is shown that the parameters r_M and χ^3/2N determine the slope of the D/D_o versus w_P relation in the strong segregation regime and the new approximation generally matches the experimental data better than the approximations used so far. Copyright © 2010 Society of Chemical Industry     

Application of the biodegradable diblock copolymer poly(L‐lactide)‐block‐poly(L‐cysteine): Drug delivery and protein conjugation

A novel approach to self‐assembled and shell‐crosslinked (SCL) micelles from the diblock copolymer poly(L ‐lactide)‐block‐poly(L ‐cysteine) to be used as drug and protein delivery carriers is described. Rifampicin was used as a model drug. The drug‐loaded SCL micelles were obtained by self‐assembly of the copolymer in the presence of the drug in aqueous media. Their morphology and size were studied with dynamic light scattering and field emission scanning electron microscopy. The rifampicin loading capacity and encapsulation efficiency were studied with ultraviolet–visible spectrophotometry. The drug‐release rate in vitro depended on the oxidizing and reducing environment. Moreover, a straightforward approach to the conjugation of the copolymer with bovine serum albumin (BSA) was developed, and a gel electrophoresis test demonstrated that this conjugated BSA could be reversibly released from the copolymer substrate under reducing conditions. In conclusion, this L ‐cysteine copolymer can be used in drug delivery and in protein fixation and recovery. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Long‐range‐ordered,hexagonally packed nanoporous membranes from degradable‐block‐containing diblock copolymer film templates

Polystyrene (PS)‐b‐polylactide (PLA) diblock copolymers with different molecular weights and fractions were synthesized through a combination of living anionic polymerization and controlled ring‐opening polymerization. Then, the PS–PLA films were guided to phase‐separate by self‐assembly into different morphologies through casting solvent selection, solvent evaporation, and thermal and solvent‐field regulation. Finally, perpendicularly oriented PS–PLA films were used as precursors for PS membranes with an ordered periodic nanoporous structure; this was achieved by the selective etching of the segregated PLA domains dispersed in a continuous matrix of PS. Testing techniques, including IR, ¹H‐NMR, gel permeation chromatography, scanning electron microscopy (SEM), and atomic force microscopy (AFM), were used to determine the chemical structure of the PS–PLA copolymer and its film morphology. AFM images of the self‐assembled PS‐PLA films indicate that vertical tapers of the PLA domains were generated among PS continuum when either toluene or tetrahydrofuran was used as the annealing solvent. The SEM images certified that the chemical etching of the PLA component from the self‐assembled PS–PLA films led to a long‐range‐ordered array of hexagonally packed nanoporous membranes with a diameter about 500 nm and a center‐to‐center distance of 1700 nm. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39638.     

Amphiphilic diblock copolymers containing poly(N‐hexylisocyanate): Monolayer behavior at the air–water interface

The behavior of amphiphilic diblock copolymers containing 80–89% of poly(N‐hexylisocyanate) (PHIC) with different hydrophobic segments spread at the air–water interface has been studied. Surface pressure‐area isotherms (π‐A) at the air–water interface were determined. It was found that these diblock copolymers form stable monolayers and the isotherms present a pseudoplateau region at low surface pressure, irrespective of the nature of the partner block: poly(styrene) (PS) or poly(isoprene). Surface pressure variation at the semidilute region of the monolayer was expressed in terms of the scaling laws as power function of the surface concentration. The critical exponents of the excluded volume ν obtained for copolymers with PHIC and PS blocks are 0.58 for the copolymer with 85% of PHIC and 15% of PS, and 0.63 for the copolymer with 89% of PHIC and 11% of PS. The hydrophobicity degree of the diblock copolymers was estimated from the determination of the surface energy values by wettability measurements. The morphology of the monolayers was determined by means of Brewster angle microscopy. Molecular dynamic simulation was performed to explain the experimental behavior of diblock copolymers at the air–water interface. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Self‐assembled honeycomb polyurethane nanofibers

Electrospinning uses a high voltage electric field to produce fine fibers. A new phenomenon of self‐assembly in the electrospinning of polyurethane nanofibers is observed. This report is the first known self‐assembling phenomenon in polyurethane electrospun nanofibers. Electrospun polyurethane nanofibers self‐assemble into unique honeycomb patterns on the collector surface. This novel observation opens up new and interesting opportunities for electrospun fibers in the areas of drug delivery devices, protective clothing, filters, and tissue scaffolds. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3121–3124, 2006     

Characterisation of block copolymer self‐assemblies by thermal field‐flow fractionation

The ability of block copolymers to self‐assemble into various nanostructures (such as micelles) has attracted significant attention over the years as these block copolymers provide a versatile platform that can readily be modified for a wide range of applications. As such, the solution behaviour of block copolymers has been at the forefront of the modern nanotechnology revolution. However, these novel block copolymer‐based self‐assemblies lack suitable characterisation techniques to determine size, molar mass and compositional distributions simultaneously. This mini‐review gives a short background on the current techniques used to determine important micelle properties as well as their limitations for characterising complex samples. Current column‐based fractionation techniques used for determining property distributions are addressed. As a result of the limitations of column‐based fractionations, a multidetector thermal field‐flow fractionation (ThFFF) approach is put forward as a powerful alternative for determining not only size and molar mass distributions, but also other micelle properties as a function of temperature. More importantly, ThFFF is highlighted as the only current characterisation platform capable of addressing the analytical challenges associated with compositional distributions of polymer self‐assemblies. © 2017 Society of Chemical Industry     

Self‐assembled polypyrrole film by interfacial polymerization for supercapacitor applications

A facile interfacial synthesis strategy is proposed to synthesize self‐assembled polypyrrole (PPy) free‐standing films for electrochemical capacitors with the assistance of surfactants. The chemical structure of the obtained samples is characterized by Fourier transform infrared. The morphologies of the samples are studied by scanning electron microscope. The results show that the prepared PPy films own highly porous structures using Tween80 as a surfactant, while the synthesized PPy films have vesicular structures by adding Span80 as a surfactant. Furthermore, lowering polymerization temperature makes PPy films have smaller and more pores or vesicles. The PPy films prepared at 0°C with Tween80 as a surfactant possess a high specific capacitance of 261 F g^?1 at 25 mV s^?1 as well as retain 75% of the initial specific capacitance value after 1000 cycles. The good electrochemical properties can be attributed to the highly porous structural advantage of the PPy films caused by Tween80. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41615.     

Selective etching of polylactic acid in poly(styrene)‐block‐poly(d,l)lactide diblock copolymer for nanoscale patterning

Self‐assembled thin films of a lamellar forming polystyrene‐block‐poly(d,l )lactide (PS‐b‐PLA) block copolymer (BCP) contain a “reactive” block that can be readily removed to provide a template for substrate pattern formation. Various methods of PLA removal were studied here with a view to develop the system as an on‐chip etch mask for substrate patterning. Solvo‐microwave annealing was used to induce microphase separation in PS‐b‐PLA BCP with a periodicity of 34 nm (L_o) on silicon and silicon on insulator (SOI) substrates. Wet etches based on alkaline and enzymatic solutions were studied in depth. Fourier transform‐infrared (FT‐IR) analysis showed that basic hydrolysis using sodium hydroxide (NaOH) or ammonium hydroxide (NH₄OH) solutions resulted in greater PLA removal in comparison to an enzymatic approach using Proteinase K in a Tris‐HCl buffer solution. However, in the enzymatic approach, the characteristic self‐assembled fingerprint patterns were retained with less damage. Comparison to a dry etch procedure using a reactive ion etch (RIE) technique was made. A detailed study of the etch rate of PS and PLA homopolymer and PS‐b‐PLA shows depending on DC bias, the etch selectivity of PLA and PS can be almost doubled from 1.7 at DC bias 145 V to 3 at DC bias 270 V. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40798. Together with Krebs et al., J. Appl. Polym. Sci. (2014) 131 , 40795, doi: 10.1002/app.40795 , this article is part of a Special Issue on Polymers for Microelectronics. The remaining articles appear in J. Appl. Polym. Sci. (2014) volume 131 , issue 24. This note was added on 1st July 2014.     

Dewetting and microphase separation in symmetric polystyrene‐block‐polyisoprene diblock copolymer ultrathin films

The kinetics of surface structure evolution in ultrathin films of low‐molecular‐weight polystyrene‐block‐polyisoprene (M_w: 7300 g mol^?1–7300 g mol^?1) diblock copolymer at temperatures below the bulk order‐to‐disorder transition temperature are presented. Films with two different thicknesses were studied as a function of annealing temperature using atomic force microscopy. These film thicknesses enabled the investigation of the competition between microphase separation and dewetting that resulted in two different morphologies: long‐range bicontinuous structures and random holes. Three distinctive stages of structure evolution were observed in bicontinuous structure, with the underlying mechanism compared with spinodal dewetting. Thicker films presented holes on their surfaces upon annealing at elevated temperatures, and kinetics of formation of the holes were discussed. We found that the molecular mobility determined the rates of dewetting, while the microphase separation hardly affected the dewetting process. © 2015 Society of Chemical Industry     

Self‐assembling amphiphilic PEGylated block copolymers obtained through RAFT polymerization for drug‐delivery applications

In this work, ring‐opening polymerization and reversible addition‐fragmentation chain transfer polymerization (RAFT) have been employed for the production of block copolymers where the backbone is brushed with poly(ethylene glycol) (PEG) and polyester chains. Because of their amphiphilic properties, they are able to self‐assemble in water, forming micelles. Molecular dynamics simulations have been accomplished to study the behavior of the copolymer single chain in water, and the self‐assembly properties have been characterized and correlated to the copolymer structure in terms of critical micellar concentration and particle size. As a proof of their flexibility, these materials have been employed for the production of polymer–lipid hybrid nanoparticles with tunable dimensions (from 120 to 260 nm) adopted for the controlled release of anticancer compounds (paclitaxel and curcumin). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43084.     

Fabrication of Amino‐Terminated Multiwalled Carbon Nanotubes via Layer‐by‐Layer Self‐Assembly Approach

MWCNT‐based composites have been successfully synthesized via layer‐by‐layer self‐assembly of crosslinked polyphosphazene nanoparticles on the surface of MWCNTs. The amino‐terminated CNTs were characterized by XPS, FT‐IR spectroscopy, EDS, XRD and TEM. The degree of functionalization could be controlled by simply changing the mass of hexachlorocyclotriphosphazene with 4,4′‐diaminodiphenyl ether. The activity of the surface amino groups was confirmed by the reaction of these groups with HAuCl₄. In addition, the effects of the mass of HCCP and ODA ratios on the content of the surface amino groups was also investigated.

     

Hydrogen bond‐mediated self‐assembly and supramolecular structures of diblock copolymer mixtures

This review summarizes recent advances in the preparation of hydrogen bonding block copolymer mixtures and the supramolecular structures they form through multiple hydrogen bonding interactions. Hydrogen bonding in block copolymer mixtures that form nanostructures and have unusual electronic, photonic and magnetic properties is a topic of great interest in polymer science. Combining the self‐assembly of block copolymers with supramolecular structures offers unique possibilities to create new materials with tunable and responsive properties. The self‐assembly of structures from diblock copolymer mixtures in the bulk state is readily controlled by varying the weight fraction of the block copolymer mixture and the copolymer composition; in solution, the morphologies are dependent on the copolymer composition, the copolymer concentration, the nature of the common solvent, the amount of the selective solvent and, most importantly, the hydrogen bonding strength. Copyright © 2008 Society of Chemical Industry     

Clustered assembly of Au nanoparticles from spherical diblock copolymer micelles encapsulating Au nanoparticle

Superstructures composed of diblock copolymer micelles and inorganic nanoparticles are quite interesting because the specific arrangement of inorganic nanoparticles within the micellar structure can reveal interesting opportunities in many field of science. In this perspective, we report a simple method to produce clustered assembly of Au nanoparticles in the micelles in attempt to induce plasmonic coupling among multiple Au nanoparticles in the assembled structures. Here, we utilized polystyrene‐block‐poly(acrylic acid), PS‐PAA, micelles containing single Au nanoparticle in the core (Au@PS‐PAA micelles) as building materials to initiate next‐level assembling process. In particular, the addition of HCl to the solution of Au@PS‐PAA micelles affected the overall equilibrium condition as well as kinetic process in the micellar solution. As a result, individual Au@PS‐PAA micelles could be merged together to form more large micelles with inclusion of multiple nanoparticles in the core, the process of which was accompanied with plasmonic coupling of Au nanoparticles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44693.     

Synthesis of poly(vinyl acetate) containing diblock copolymer by DPE method

Diblock copolymer poly(methyl methacrylate)‐b‐poly(vinyl acetate) (PMMA‐b‐PVAc) was prepared by 1,1‐diphenylethene (DPE) method. First, free‐radical polymerization of methyl methacrylate was carried out with AIBN as initiator in the presence of DPE, giving a DPE containing PMMA precursor with controlled molecular weight. Second, vinyl acetate was polymerized in the presence of the PMMA precursor and AIBN, and PMMA‐b‐PVAc diblock copolymer with controlled molecular weight was obtained. The formation of PMMA‐b‐PVAc was confirmed by ¹H NMR spectrum. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to detect the self‐assembly behavior of the diblock polymer in methanol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Self‐assembled nanoblends of functional polystyrene and a reactive aramid: Morphological and thermomechanical profile

Various blends composed of pure polystyrene (PS) and modified PS [amino‐functionalized polystyrene (PS–NH₂)] were prepared with a new aromatic polyamide obtained through the polycondensation of 1,5‐diaminonaphthalene and 1,4‐phenylenediamine with isophthaloyl chloride. The variation in the morphological and thermophysical profiles in the two blend systems with aramid loading were investigated. The amine functionality introduced to PS enhanced its compatibility with the polyamide because of the formation of an aramid‐graft‐PS copolymer. The grafting, hydrogen bonding, and phenylene‐ring (π–π) stacking between the chains of the two components finally nurtured self‐assembled nanostructured blends. A strong compatibilizing effect was observed for the 50, 60, and 70 wt % aramid blends, where an exceptionally inimitable cocontinuous self‐assembled morphology was formed by PS–NH₂/aramid. Significant developments in the morphology along with thermal and mechanical stability were observed for the reactive PS/aramid system. The most favorable mechanical and thermal data supported by the finest nanostructure were observed with 70 wt % polyamide addition. Future prospects may involve the formation of nanotemplates and nanostructured membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39954.     

Self‐assembled poly(styrene‐co‐N‐isopropylacrylamide) film induced by capillary force

The monodisperse poly(styrene‐co‐N‐isopropylacrylamide) (poly(St‐co‐NIPAAm)) particles prepared by emulsifier‐free emulsion polymerization with microwave irradiation were induced by capillary forces to self‐assemble, and formed the two‐dimensional films on the clean glassware wafer substrates. The morphologies of the two‐dimensional films were characterized by scanning electron microscopy (SEM) and atom force microscopy (AFM). The results showed that monodisperse poly(St‐co‐NIPAAm) particles could form ordered two‐dimensional films by capillary forces. With NIPAAm concentration increasing, there gradually appeared surface undulations or surface defective region on the two‐dimensional films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3514–3519, 2006