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The ion specificity effect on the water solubility of poly(N-isopropylacrylamide)-containing copolymers complies with the Hofmeister series, which is applicable to other copolymers or not need to be explored. In this work, effects of ionic strength under acidic conditions and ion specificity under alkaline conditions on the air/water interface behavior of two amphiphilic diblock copolymers poly(dimethylaminoethyl methacrylate)-poly(lauryl methacrylate) (PDMAEMA-PLMA) were systematically studied. Under acidic conditions, the surface pressure-area isotherms of a predominantly hydrophilic copolymer are insensitive to ionic strength. In contrast, the isotherms of a predominantly hydrophobic copolymer successively shift to the large, small, and large molecular area with the increase of ionic strength. Under alkaline conditions, the interfacial stretch degrees of PDMAEMA chains of two copolymers change with salt species and concentrations, which do not comply with the Hofmeister series. All of the Langmuir-Blodgett films of the former copolymer exhibit separate circular micelles. Nevertheless, those of the latter copolymer obtained under alkaline conditions exhibit various distinctive morphologies such as separate circular micelles, large separate PLMA cores within large PDMAEMA domains, and large PLMA domains/aggregates surrounded by short PDMAEMA shells. It can be attributed to the high deformability of PLMA chains, the ion specificity effect on the stretch degree of PDMAEMA blocks, and their underwater solubility upon compression.

At the air/water interface, amphiphilic block copolymers are well-known to form typical surface micelles composed of hydrophobic block cores and hydrophilic block coronas. However, the micelle/aggr...

The Langmuir film balance technique was used to investigate the effects of copolymer composition and subphase pH/temperature on the aggregation behaviors of two stimuli-responsive amphiphilic diblo...

In recent years, the dewetting behavior of block copolymer films has been studied a lot, but that of random copolymer films was rarely studied. In this study, effects of film thickness and solvent vapor annealing duration (0 s-24 h) on the dewetting behavior of the spin-coated poly(styrene- co -acrylonitrile) (SAN) random copolymer films were mainly investigated by atomic force microscopy and contact angle method for the first time. The film thicknesses of the SAN films prepared at different concentrations were characterized by X-ray reflectometry to be 6-34 nm. With the annealing of acetone vapor, the SAN films first appear holes and then rupture into droplets which fuse and break periodically. The periodic evolutions of the droplets are due to the preferred affinity of acetone molecules with the AN segments and the change of surface energy. This phenomenon is different from the single evolutions in the spin-coated polystyrene- block -poly(methyl methacrylate) (PS- b -PMMA) block copolymer films. This illustrates the interactions between AN segments and the substrate are stronger than those between PMMA segments and the substrate in the spin-coated films.

Aggregation behaviors of the blended Langmuir monolayers of a homopolymer polystyrene (h-PS) and a triblock copolymer polystyrene-b-poly(ethylene oxide)-b-polystyrene (PS-b-PEO-b-PS) were studied by the Langmuir film balance technique, and the morphologies of their Langmuir–Blodgett (LB) films were studied by atomic force microscopy. The isotherms of the h-PS/PS-b-PEO-b-PS blends shift to small areas with the increase of h-PS content, and a pseudoplateau appears as h-PS content is below 60 wt %. It is worth noting that the blended isotherms appear at the left of their corresponding ideal ones, which means that the blended monolayers are a little more condensed due to attractive interactions between the two components. Hysteresis phenomena exist in all of the blended monolayers, and the higher the PS-b-PEO-b-PS content, the larger the hysteresis degree becomes because of the stronger looped-PEO entanglements. All the blended LB films of h-PS and PS-b-PEO-b-PS prepared under low pressure exhibit the mixed s...

Aggregation behavior of an amphiphilic diblock copolymer poly(lauryl acrylate)-block-poly(N-isopropylacrylamide) (PLA-b-PNIPAM) on neutral aqueous subphases with different salt species and salt concentrations, as well as the structures of its Langmuir-Blodgett (LB) films, were systematically studied. The presence of NaCl or Na2SO4 in subphases makes PNIPAM chains shrink on the water surface and reduce their solubility underwater. On the contrary, the presence of NaNO3 or NaSCN makes PNIPAM chains more stretched on water and increase their solubility underwater, whose stretch degree and solubility both increase with the increase of salt concentration. Solubility of PNIPAM chains in the above subphase solutions is ranked as NaSCN ≫ NaNO3 > pure H2O > NaCl ≈ Na2SO4, which is almost consistent with the Hofmeister series except for the latter two close cases. All the initial LB films of PLA-b-PNIPAM exhibit tiny isolated circular micelles. Upon compression, the LB films in the case of pure H2O exhibit the dense mixed structures of circular micelles and wormlike aggregates. The formation of wormlike aggregates is due to connection of some adjoining cores, which is less possible in other subphase cases because of the conformation difference of PNIPAM chains.

Aggregation behavior of an amphiphilic diblock polyelectrolyte poly(n-butylacrylate)-b-poly(acrylic acid) (PnBA-b-PAA) at the air/water interface and its Langmuir−Blodgett (LB) films were respectively characterized by the Langmuir film balance technique and atomic force microscopy. Effects of spreading solution concentration and volume, and subphase temperature and ionic strength on the interfacial aggregation behavior of PnBA-b-PAA under alkaline condition were systematically studied. With the increase of spreading concentration, surface pressure−molecular area isotherms shift to small molecular areas at the corresponding spreading volumes. With the rise in subphase temperature, the isotherms shift to small molecular areas due to the decreased pKa value and increased solubility of PAA blocks. With the increase of subphase ionic strength, the isotherms shift to large molecular areas because of the predominant salting out effect. The LB films transferred from alkaline subphase with different ionic strengths are more likely to exhibit isolated circular micelles. With the increase of spreading concentration, diameters of micelle cores first decrease and then increase, a behavior which is attributed to the gradually increased chain entanglements and surface polymer concentration, respectively. For small spreading volume, core diameters in the LB films first decrease and then increase with the rise in subphase temperature. For large spreading volume, however, core diameters increase with temperature due to the higher mobility and weaker entanglements of PAA blocks underwater. With the increase of subphase ionic strength, furthermore, core diameters first increase and then decrease, which is attributed to the predominant electrostatic shielding and salting out effects, respectively.

Effects of subphase pH and temperature on the aggregation behavior of a thermosensitive amphiphilic diblock copolymer poly(lauryl acrylate)-block-poly(N-isopropylacrylamide) (PLA-b-PNIPAM) at the a...

Langmuir monolayers and Langmuir-Blodgett (LB) films of a symmetric diblock copolymer polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) were characterized by the film balance technique and tapping mode atomic force microscopy, respectively. Effects of both the spreading solution concentration and the surface concentration on the aggregation behavior of PS- b-PMMA at the air/water interface and the morphologies of its LB films were studied in detail. When the monolayers spread in different concentrations (≤0.50 mg/mL), all their initial morphologies exhibit tiny circular micelles because of the long hydrophilic PMMA block in the copolymer. The initial tiny circular micelles form spontaneously and then aggregate into small ones upon compression, which can further coalesce into rodlike aggregates or large micelles depending on the spreading concentrations. The LB films of PS- b-PMMA usually exhibit various mixed structures of rodlike aggregates and circular micelles, which can further transform into labyrinth patterns under some special spreading conditions. Besides spreading concentration and volume, we discover that the detailed spreading process should also be responsible for the initial and final morphologies of the LB films. Furthermore, the LB films prepared under different spreading conditions can be regarded as in the equilibrium or nonequilibrium structures because of the kinetic effect difference resulting from the different PS chain entanglement degrees.

We previously reported that poly(acrylic acid) (PAA) blocks at the air/water interface spontaneously immersed into water at high pH before monolayer compression. To investigate the influence of the hydrophobic methyl groups in poly(methacrylic acid) (PMAA) blocks, in this work, subphase pH and temperature effects on the aggregation behaviors of two pH-responsive amphiphilic diblock copolymers poly(lauryl methacrylate)-block-poly(methacrylic acid) (PLMA-b-PMAA) (PLMA49%-PMAA and PLMA61%-PMAA, composition in weight percent) at the air/water interface were studied. The surface pressure–molecular area isotherms of the two copolymers move to small mean molecular area (mma) as subphase pH increases and a quasi-plateau exists under various subphase conditions, which is quite different from its absence in our previous PAA-containing block copolymer system. The quasi-plateau is attributed to the pancake-to-brush transition as non-ionized PMAA chains submerge into subphase upon monolayer compression. Under acidic condition, PMAA chains of the two copolymers are almost non-ionized, the compression and expansion isotherms show large hysteresis phenomena. Under neutral and alkaline conditions, the isotherms show small hysteresis, which is because more ionized PMAA chains immerse in subphase before compression. The isotherms shift toward small mma with increasing temperature under neutral and alkaline conditions, whereas a slight shift back to large mma is observed under acidic conditions. The plateau surface pressures of the two PLMA-b-PMAA copolymers decrease with increasing temperature under different pH conditions, which is because the micelles move more freely and easier to rearrange at high temperature. The plateau surface pressures of PLMA49%-PMAA are higher than those of PLMA61%-PMAA under the corresponding conditions due to the higher PMAA content in the former. The initial Langmuir–Blodgett (LB) films of the two copolymers transferred under different pH conditions at various temperatures exhibit isolated circular micelles because of the steric hindrance and/or repulsive interactions among the long PMAA chains. Furthermore, temperature has almost no effect on the micelle core diameters of the initial LB films.

Aggregation behaviors of the blended Langmuir monolayers of a homopolymer polystyrene (h-PS) and a triblock copolymer polystyrene

Aggregation behavior of an amphiphilic diblock copolymer poly(lauryl acrylate)

We once studied the dewetting behaviors of spin-coated and Langmuir−Blodgett (LB) films of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) induced by solvent vapor annealing (SVA), and revealed the different contact degrees between hydrophilic PMMA blocks and the substrate in the above two kinds of films. In this work, the dewetting behavior of self-assembled films of PS-b-PMMA induced by SVA was studied for the first time. Effects of copolymer composition, solution concentration, and SVA time were systematically considered. With the increase of SVA time, continuous flat self-assembled films undergo complicated progresses including the formation of bicontinuous or holed structures, the formation of droplets, and the periodic increase and decrease of droplet sizes. The periodic evolutions of droplet sizes in the self-assembled films are similar to those in our previous LB films but different from their single evolutions in the spin-coated films. It indicates that the former two kinds of films have good contact degrees between PMMA blocks and the substrate. Furthermore, the contact degrees in the self-assembled films are better than those in the LB films. In our current minds, the contact degrees are mainly related to the length of hydrophilic blocks and their parallel/vertical segment ratio to the substrate.

Aggregation behavior of an amphiphilic diblock polyelectrolyte poly(n-butylacrylate)-b-poly(acrylic acid) (PnBA-b-PAA) at the air/water interface and morphologies of its LB films were characterized by the Langmuir monolayer technique and atomic force microscopy (AFM), respectively. Effects of subphase pH, temperature and ionic strength on the isotherms and hysteresis curves of the PnBA-b-PAA monolayers and the morphologies of its LB films were systematically studied. With the increase of subphase pH, the isotherms shift negatively and the quasi-plateaus disappear under neutral and alkaline conditions. Hysteresis phenomena of the PnBA-b-PAA monolayers on acidic and neutral subphases are quite obvious and similar, while the compression and expansion isotherms under alkaline condition are almost overlapped. The LB films of PnBA-b-PAA transferred from acidic subphase exhibit isolated circular micelles with large size, while those from alkaline subphase exhibit condensed ones with small size. With the rise in subphase temperature, PnBA blocks on the water surface are more likely to aggregate into large cores due to the higher molecular mobility. Furthermore, the totally ringlike nanostructures prepared from alkaline subphase with medium ionic strength are observed for the first time in LB films of block copolymers.

A selective solvent was used to study the aggregate behavior of mixed Langmuir monolayers of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) and polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). A peculiar hysteresis phenomenon is reported for the first time, in which the expansion curves cross their corresponding compression curves, and the final surface pressures after the expansion processes are significantly higher than, instead of close to, their initial compression values. The mixed Langmuir–Blodgett (LB) films exhibit more mixed circular micelles and fewer mixed rod-like aggregates with the increase of the PS-b-PEO content, which is quite different from those that only exhibit mixed circular micelles by using a nonselective solvent. So far we have carried out the progressive morphology evolution and the aggregate density control in the mixed LB films by using the selective spreading solvent and adjusting the blend composition and transfer pressure, which is an interesting way to control and design morphology into an ultrathin film for some applications such as nanopatterns and nanotemplates.

In order to explore the aggregation mechanisms of mixed polymeric Langmuir monolayers and enrich the structures of their corresponding Langmuir–Blodgett (LB) films, a predominantly hydrophilic triblock copolymer polystyrene-block-poly(ethylene oxide)-block-polystyrene (SEOS69K, Mn = 69 000, 43.5 wt% PEO) was mixed with an amphiphilic diblock copolymer polystyrene-block-poly(methyl methacrylate) (SMMA34K, Mn = 33 500, 26.9 wt% PMMA). The Langmuir monolayers and LB films of SEOS69K, SMMA34K, and their blends were characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. The isotherms of the samples deviate to large areas with the increase of the SEOS69K content and exhibit pseudo-plateaus for the samples with above 80 wt% SEOS69K. The hysteresis degree of the mixed Langmuir monolayer with 80 wt% SEOS69K compressed up to 30 mN m−1 is significantly larger than that with 20 wt% SEOS69K, which can be interpreted by a reasonable schematic illustration combining the predominant PEO and the few PEO/PMMA chain entanglements in the former with the low mobility of PEO and PMMA blocks. The mixed LB films with 10 wt% SEOS69K transferred at different pressures exhibit mixed structures of circular micelles and rod-like aggregates. However, all the other mixed LB films only exhibit circular micelles composed of PS cores and mixed PEO/PMMA coronas. Upon compression, the large close-packed aggregates split into small ones with more uniform sizes, which shows that the addition of SEOS69K can really improve the structure homogeneity of the mixed LB films. Moreover, a very simple formula was deduced to transform the isotherm of a mixed Langmuir monolayer as a function of a certain copolymer molecule area or repeating unit area.

The mixed Langmuir monolayers and Langmuir-Blodgett (LB) films of homo-polystyrene (h-PS) and the diblock copolymer polystyrene-block -poly(2-vinylpyridine) (PS-b-P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h-PS is below 80 wt.-%, the mixed LB films of h-PS/PS-b-P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h-PS content (80-95%), however, highly uniform and stable necklace-network structures are observed in the mixed LB films.

Langmuir monolayers of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers (with the same PS block length and different P2VP block lengths) formed at the air/water interface were characterized with the Langmuir film balance technique. Nonselective and selective solvents were used to spread the samples on the water surface and the spreading solvents showed large effect on the surface pressure–molecular area isotherms. The corresponding Langmuir–Blodgett (LB) films of the samples were characterized with atomic force microscopy. The LB films transferred from the Langmuir monolayers spread with a nonselective solvent only exhibited isolated circular micelles, while those with a selective solvent exhibited quite different morphologies including planar structure, rodlike structure, circular micelles, and labyrinth pattern. As far as we know, the labyrinth pattern appears in the LB films for the first time.

The pressure-dependent glass-transition temperatures (T-g's) of poly(methyl methacrylate) (PMMA)/poly(styrene-co-acrylonitrile) (SAN) blends were determined by pressure-volume-temperature (PVT) dilatometry via an isobaric cooling procedure. The Gordon-Taylor and Fox equations were used to evaluate the relationships between the T-g's and compositions of the PMMA/SAN system at different pressures. The relationships were well fitted by the Gordon-Taylor equation, and the experimental data for T-g positively deviated from the values calculated with the Fox equation. Also, the influence of the cooling rate (during the PVT measurements) on T-g was examined.

The thin films of poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (SAN) and their blends were prepared by means of spin-coating their corresponding solutions onto silicon wafers, followed by being annealed at different temperatures. The surface phase separations of PMMA/SAN blends were characterized by virtue of atomic force microscopy (AFM). By comparing the tapping mode AFM (TM-AFM) phase images of the pure components and their blends, surface phase separation mechanisms of the blends could be identified as the nucleation and growth mechanism or the spinodal decomposition mechanism. Therefore, the phase diagram of the PMMA/SAN system could be obtained by means of TM-AFM. Contact mode AFM was also used to study the surface morphologies of all the samples and the phase separations of the blends occurred by the spinodal decomposition mechanism could be ascertained. Moreover, X-ray photoelectron spectroscopy was used to characterize the chemical compositions on the surfaces of the samples and the miscibility principle of the PMMA/SAN system was discussed.

The effects of the chain structure and the intramolecular interaction energy of an A/B copolymer on the miscibility of the binary blends of the copolymer and homopolymer C have been studied by means of a Monte Carlo simulation. In the system, the interactions between segments A, B and C are more repulsive than those between themselves. In order to study the effect of the chain structure of the A/B copolymer on the miscibility, the alternating, random and block copolymers were introduced in the simulations, respectively. The simulation results show that the miscibility of the binary blends strongly depends on the intramolecular interaction energy ( e AB ) between segments A and B within the A/B copolymers. The higher the repulsive interaction energy, the more miscible the A/B copolymer and homopolymer C are. For the diblock copolymer/homopolymer blends, they tend to form micro phase domains. However, the phase domains become so small that the blend can be considered as a homogeneous phase for the alternating copolymer/homopolymer blends. Furthermore, the investigation of the average end-to-end distance ( h ) in different systems indicates that the copolymer chains tend to coil with the decrease of e AB whereas the h of the homopolymer chains depends on the chain structure of the copolymers. As for the system containing the alternating or the random copolymers, the homopolymer chains also tend to coil with the decrease of e AB . However, for the systems including the block copolymers, there is a slight difference in the h of the homopolymer chains with the variation of e AB .

By fitting the spinodals of poly(vinyl methyl ether)/deuterated polystyrene (PVME/PSD) systems, the adjustable parameters epsilon (12)* and delta epsilon* in the Sanchez-Balasz lattice fluid (SBLF) theory could be determined for different molecular weights. According to these parameters, Flory-Huggins and scattering interaction parameters were calculated for PVME/PSD with different molecular weights by means of the SELF theory. From our calculation, Flory-Huggins and scattering interaction parameters are both Linearly dependent on the reciprocal of the temperature, and almost linearly on the concentration of PSD. Compared with the scattering interaction parameters, the Flory-Huggins interaction parameters decreased more slowly with an increase in the concentration for all three series of blends.

Our recent work showed there existed a composition window for mixed Langmuir monolayers of homopolystyrene (h-PS) and a symmetric diblock copolymer polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) to form necklace-network structures at the air/water interface. In order to study further the possible mechanism and control the network structure (i.e., surface coverage and nanoaggregate diameter), effects of spreading solution concentration and volume, subphase temperature, and transfer pressure on the network structure were studied by the Langmuir monolayer technique and tapping mode atomic force microscopy. With the increase of transfer pressure, there existed a novel nonlinear behavior for the nanoaggregate diameter first to increase, then to decrease, and finally to increase again, while the surface coverage tended to increase step by step. Moreover, with the elevation of temperature, chain motion between the adjoining nanoaggregates tended to be improved and thus the nanoaggregate diameter tended to be more uniform.