Growth of silica nanoparticles in methylmethacrylate-based water-in-oil microemulsions

The mechanism of silica particle formation in monomer microemulsions is studied using dynamic light scattering (DLS), atomic force microscopy, small-angle X-ray scattering (SAXS), and conductivity measurements. The hydrolysis of tetraethylorthosilicate (TEOS) in methylmethacrylate (MMA) microemulsions (MMA = methylmethacrylate) is compared with the formation of SiO₂ particles in heptane microemulsions. Stable microemulsions without cosurfactant were found for MMA, the nonionic surfactant Marlophen NP10, and aqueous ammonia (0.75 wt%). In the one-phase region of the ternary phase diagram, the water/surfactant ratio (R _w) could be varied from 6 to 18. The DLS and SAXS measurements show that reverse micelles form in these water-in-oil (w/o) microemulsions. The minimum water-to-surfactant molar ratio required for micelle formation was determined. Particle formation is achieved from the base-catalyzed hydrolysis of TEOS. According to atomic force microscopy measurements of particles isolated from the emulsion, the particle size can be effectively tailored in between 20 and 60 nm by varying R _w from 2–6 in heptane w/o microemulsions. For MMA-based microemulsions, the particle diameter ranges from 25 to 50 nm, but the polydispersity is higher. Tailoring of the particle size is not achieved with R _w, but adjusting the particle growth period produces particles between 10 and 70 nm.     

Vibrational spectroscopic study on the phase transition of water in nanospaces and at interfaces

Phase transition of water confined in nanospaces with charged inner-surfaces was investigated by vibrational spectroscopy. Aerosol sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles give a series of spherical nanospaces with controlled inner-radius (R_w) with nanometer-scale precision. Successive spectroscopic measurements of the confined water with decreasing temperature revealed that the water freezes to metastable cubic ice (I_c) coexisting with super-cooled water or unstable amorphous ice at the R_w ranging from 1.0 to 2.0 nm. When R_w exceeded 2.0 nm, stable hexagonal ice (I_h) dominated. The drastic change of the dominant ice structure with the increase of 1 nm in R_w shows that the thickness of water layers affected by the inner surface can be estimated to be ~1 nm, where three or four layers of water hydrated to the surface. It is worth noting that the clear phase transition behavior of the confined water vanishes at R_w = 1.2 nm and that the gradual formation of I_c and coexistence of super-cooled water or glassy state of water are detected. The range of the effective interaction between interfacial water and the charged inner surfaces and the mechanism of the extremely slow phase transition were also discussed.     

The Charging of Micellar Nanoparticles in Electrospray Ionization

Charging of nanoparticles through electrospray has scarcely been explored. Spherical nanometer‐sized amphiphilic block copolymer nanoparticles with diameters ranging from ～65 to ～150 nm were electrosprayed and analysed by charge detection spectrometry. Herein, we explore the charging of these micellar nano‐objects by conducting a thorough study in different solvents, including pure water, and upon the addition of “supercharging” agents. The charge (z) of micellar nanoparticles electrosprayed from water solution is compared to the Rayleigh’s limiting charge (z_R) of a charged water droplet of the same dimensions. An average ratio (z/z_R) of 0.6–0.65 is observed for the micellar macro‐ions, supporting the charge residue mechanism, where the number of charges available to the micellar macro‐ion is limited by the number of charges on the nanodroplet, which is a function of the surface tension of the solvent. Also we show the possibility of increasing the charging of micellar nanoparticles in the negative mode by adding organic bases (in particular piperidine) to water/methanol solutions.     

Characterization of poly(methyl methacrylate) nanoparticles prepared by nanoprecipitation using analytical ultracentrifugation,dynamic light scattering,and scanning electron microscopy

Nanoprecipitation represents an effective method for the production of polymeric nanoparticles. This technique was used to prepare nanoparticles from solutions of poly(methyl methacrylate) and its copolymers. Since the regulation of main parameters like particle size, particle size distribution, and molar particle mass is very important for future applications, the stable nanoparticle dispersions were examined by scanning electron microscopy, velocity sedimentation, and dynamic light scattering, whereby advantages and disadvantages of each characterization techniques are discussed. Polydispersities of particle size distributions are determined by the ratio of d_w/d_n, where d_w and d_n are weight‐ and number‐average diameters, respectively. The particle characteristics strongly depend on the chemical structure of the polymers and the way of preparation and, therefore, vary in the studied cases in the range of 6 < d_w < 680 nm, whereas the polydispersity index d_w/d_n changes in the range of 1.02 to 1.40. It is shown that nanoparticles in a desirable size range can be prepared by solvent–nonsolvent methods (dialysis technique or dropping technique). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3924–3931, 2010     

Structure formation of surfactants in concentrated sulphuric acid: a light scattering study

A common cationic surfactant,n-hexadecylammonium hydrogensulphate, dissolved in concentrated sulphuric acid, has been studied by static and dynamic light scattering. Micelle formation has been observed even in this unusual solvent. An apparent molar mass of 45 500±4.5% was found for the aggregates. A translational diffusion coefficientD ₀=5.5×10^–9 cm²/s was measured which gave a hydrodynamically effective radius ofR _h=17.7 nm. The geometric radius of gyration wasR _g=76.2 nm. The ratioR _g/R _h=4.33 is indicative for rodlike structures. Assuming a polydispersity ofL _w/L _n=2 this corresponds to a cylinder ofL _w=152 nm. An axial ratiop _w=(L _w/d)=60.4 nm was estimated which leads to a cylinder diameter of 2.53 nm. At surfactant concentrations higher than 5% (w/vol) the rod-like micelles aggregate to form more globular structures. The time correlation function, recorded by dynamic light scattering, exhibited a two-step decay which indicates a bimodal distribution of particle sizes. The fast motion coincides with that of the micelles at low concentrations while the other is slower than the fast one by three orders of magnitude and corresponds to the translational motion of large clusters.     

Adding sodium dodecylsulfate to the running electrolyte enhances the separation of gold nanoparticles by capillary electrophoresis

This paper describes employing capillary electrophoresis (CE) for the separation of gold colloids in nanometer-size regimes. Adding sodium dodecylsulfate (SDS) surfactant to the running buffer enhances the capability of CE to separate gold nanoparticles. We found that the optimized separation conditions involved SDS (70 mM), 3-cyclohexylamoniuopropanesulfonic acid (CAPS) buffer (10 mM), pH 10.0, and an applied voltage of 20 kV. We propose that the charged surfactants associate onto the surface of the gold nanoparticles and cause a change in the charge-to-size ratio of gold nanoparticle, which is a function of the surface area of nanoparticle and the surfactant concentration of running electrolyte. At high concentrations of the surfactant in the running electrolyte—i.e., when the surface of the gold nanoparticles is fully occupied with SDS—a linear relationship exists between the electrophoretic mobility and nanoparticles having diameters ranging from 5.3 to 38 nm. Based on the results of separating the 5.3 and 19 nm nanoparticles, we estimate that the size resolution (R_s=1.0) is 5.0 nm. The relative standard deviations of the electrophoretic mobilities of the 5.3 and 19 nm gold nanoparticles are 0.97 and 0.54%, respectively.     

Transmission electron microscopy characterization of colloidal copper nanoparticles and their chemical reactivity

A colloidal synthesis method was developed to produce face centered cubic (fcc) Cu nanoparticles in the presence of surfactants in an organic solvent under an Ar environment. Various synthetic conditions were explored to control the size of the as-prepared nanoparticles by changing the precursor, varying the amount of surfactants, and tuning the reaction temperature. Transmission electron microscopy (TEM), selected-area electron diffraction, and high-resolution TEM were used as the main characterization tools. Upon exposure to air, these nanoparticles are oxidized at different levels depending on their sizes: (1) an inhomogeneous layer of fcc Cu₂O forms at the surface of Cu nanoparticles (about 30 nm); (2) Cu nanoparticles (about 5 nm) are immediately oxidized into fcc Cu₂O nanoparticles (about 6 nm). The occurrence of these different levels of oxidization demonstrates the reactive nature of Cu nanoparticles and the effect of size on their reactivity. Furthermore, utilization of their chemical reactivity and conversion of spherical Cu nanoparticles into CuS nanoplates through the nanoscale Kirkendall effect were demonstrated. The oxidization and sulfidation of Cu nanoparticles were compared. Different diffusion and growth behaviors were involved in these two chemical transformations, resulting in the formation of isotropic Cu₂O nanoparticles during oxidization and anisotropic CuS nanoplates during sulfidation.      

Study on soap‐free P(MMA‐EA‐AA or MAA) latex particles with narrow size distribution

Soap‐free poly(methyl methacrylate‐ethyl acrylate‐acrylic acid or methacrylic acid) [P(MMA‐EA‐AA or MAA)] particles with narrow size distribution were synthesized by seeded emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA) and acrylic acid (AA) or methacrylic acid (MAA), and the influences of the mass ratio of core/shell monomers used in the two stages of polymerization ([C/S]_w) and initiator amount on polymerization, particle size and its distribution were investigated by using different monomer addition modes. Results showed that when the batch swelling method was used, the monomer conversion was more than 96.0% and particle size distribution was narrow, and the particle size increased first and then remained almost unchanged at around 600 nm with the [C/S]_w decreased. When the drop‐wise addition method was used, the monomer conversion decreased slightly with [C/S]_w decreased, and large particles more than 750 nm in diameter can be obtained; with the initiator amount increased, the particle size decreased and the monomer conversion had a trend to increase; the particle size distribution was broader and the number of new particles was more in the AA system than in the MAA system; but the AA system was more stable than the MAA system at both low and high initiator amount. Copyright © 2006 John Wiley & Sons, Ltd.     

Preparation of monodisperse nanoparticles containing poly(propylene imine)(NH2)32‐polystyrene

Polypropylenimine dendrimer (DAB‐Am‐32, generation 4.0) was converted into a macroinitiator DAB‐Am‐32‐Cl via reaction with 2‐chloropropionyl chloride. Monodisperse nanoparticles containing poly(propylene imine)(NH₂)₃₂‐polystyrene were prepared by emulsion atom transfer radical polymerization (ATRP) of styrene (St), using the DAB‐Am‐32‐Cl/CuCl/bpy as initiating system. The structure of macroinitiator was characterized by FTIR spectrum, ¹H NMR, and ¹³C NMR. The structure of poly(propylene imine)(NH₂)₃₂‐polystyrene was characterized by FT‐IR spectrum and ¹H NMR; the molecular weight and molecular weight distribution of poly(propylene imine)(NH₂)₃₂‐polystyrene were characterized by gel permeation chromatograph (GPC). The morphology, size and size distribution of the nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The effects of monomer/macroinitiator ratio and surfactant concentration on the size and size distribution of the nanoparticles were investigated. It was found that the diameters of the nanoparticles were smaller than 100 nm (30–80 nm) and monodisperse; moreover, the particle size could be controlled by monomer/macroinitiator ratios and surfactant concentration. With the increasing of the ratio of St/DAB‐Am‐32‐Cl, the number‐average diameter (D_n), weight‐average diameter (D_w) were both increased gradually. With enhancing the surfactant concentration, the measured D_h of the nanoparticles decreased, while the polydispersity increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2892–2904, 2009     

Preparation of reactive polymeric nanoparticles (RPNPs)

A series of reactive polymeric nanoparticles (RPNPs) was prepared by free radical nonlinear copolymerization of mono (M ₁) and trivinyl acrylic (M ₂) monomers in miniemulsion. The crosslinking density was determined by the mole ratio of the trivinyl component. It was found that the unswelled latex nanoparticles showed a narrower dispersity than in the organic solution of macromolecules. In latex, the size increased with the ratio of M ₂ monomer due to its higher polarity in the aqueous medium. However, the swollen nanoparticles, dissolved or dispersed in organic solvent, showed a higher dispersity as a function of composition and the crosslinking density. The residual vinyl groups adjacent to the nanoparticles were subjected to further crosslinking reactions. The reactive vinyl groups were detected by nuclear magnetic resonance spectroscopy (NMR). The size of particles in swollen state was determined by dynamic laser light scattering (DLS) method and the dried form by scanning electron microscopy (SEM). It was found that size of RPNPs is in the range of 50 to 500 nm. These particles possess properties that may allow their application in areas as disparate as dental filling material and as a component in industrial powder-based coatings.     

Preparation and properties of novel cross-linked fluoroalkyl end-capped cooligomeric nanoparticles possessing double decker-type aromatic silsesquioxane segments as core units

Cross-linked fluoroalkyl end-capped cooligomers possessing double decker-type aromatic silsesquioxane segments as core units [R_F-(Ar-SiSQ) _x -(Co-M) _y -R_F] were prepared under mild conditions by the cooligomerizations of fluoroalkanoyl peroxide with the corresponding aromatic silsesquioxane possessing bifunctional vinyl groups (Ar-SiSQ) and comonomers (Co-M) such as acryloylmorpholine (ACMO), N,N-dimethylacrylamide (DMAA) and N-(1,1-dimethyl-3-oxobutyl)acrylamide (DOBAA). Interestingly, these cross-linked fluorinated cooligomers thus obtained were found to form the nanometer size-controlled nanoparticles with a good dispersibility in a variety of solvents including fluorinated aliphatic solvents. These fluorinated cooligomeric nanoparticles were demonstrated to have red-shifted fluorescent emissions related to the presence of aromatic silsesquioxane segments, compared with that of parent aromatic silsesquioxane, indicating that each aromatic moiety in these nanoparticles can interact effectively with each other through the π–π stacking between the aromatic moieties to afford the red-shifted fluorescent emissions. These fluorinated nanoparticles were also applied to the surface modification of poly(methyl methacrylate) (PMMA) to exhibit not only a good oleophobicity imparted by fluorine but also a fluorescent emission behavior related to aromatic silsesquioxane segments in nanoparticles on the modified PMMA surface. More interestingly, cross-linked R_F-(Ar-SiSQ) _x -(DOBAA) _y -R_F cooligomeric nanoparticles interacted with fluorescein to give the corresponding fluorinated cooligomeric particles/fluorescein nanocomposites in methanol. These fluorinated fluorescein nanocomposites were found to afford an extraordinarily enhanced light absorption (λ _max = 441 nm), compared with that of fluoroalkyl end-capped DOBAA oligomer [R_F-(DOBAA) _n -R_F] possessing no aromatic silsesquioxane segments.     

Direct low-temperature synthesis of RB6 (R=Ce, Pr, Nd) nanocubes and nanoparticles

Rare-earth hexaborides (RB₆, R=Ce, Pr, Nd) nanocrystals were prepared by a facile solid state reaction in an autoclave. Single-crystalline RB₆ nanocubes were fabricated at 500 °C starting from B₂O₃, RCl₃·6H₂O and Mg powder. RB₆ nanoflakes and nanoparticles could be obtained around 400 °C using NaBH₄ as boron resource. XRD patterns show that all of the hexaborides are cubic phase with high crystallinity and high purity and have lattice parameters that are consistent with nearly stoichiometric products. Raman spectra elucidate the active vibrational modes of the hexaborides. The TEM and FESEM images clearly show that the nanocubes have an average size of 200 nm and nanoparticles of 30 nm. Our experiment developed an efficient, simple and low-cost route to prepare RB₆, which could be extended further to the preparation of other rare-earth metal hexaborides.     

Physicochemical Investigation of the Micellar Behavior of a Diblock (PEO)62-b-(PBO)33 Copolymer in Water and its Interaction with Ionic Surfactants

The physicochemical investigations on the associative, micellar, and thermodynamic properties of a diblock (PEO)₆₂-b-(PBO)₃₃ copolymer in aqueous medium and its interaction with ionic surfactants were carried out by using surface tensiometry, laser light scattering, and steady-state fluorescence spectroscopy. Surface tension and fluorescence measurements were used to find out the critical micelle concentration (CMC) and related thermodynamic parameters of micellization copolymer at various temperatures. The data from dynamic light scattering (DLS) were helpful to obtain the values of hydrodynamic radii (R_h), volume (υ_h), and hydrodynamic expansion parameter (δ_h) of the copolymer micelle. Likewise, the measurements from static light scattering (SLS) were employed to determine weight-average molar (M_w), association number (N_w), thermodynamic radius (R_t), thermodynamic volume (υ_t), anhydrous volume (υ_a), and thermodynamic expansion parameter (δ_t) of the copolymer micelles in the temperature range of 20–50°C. Similarly, the interactions between (PEO)₆₂-b-(PBO)₃₃ and two ionic surfactants, sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB), have also been investigated by fluorescence spectroscopy and DLS at 30°C. Similarly, the interactions between (PEO)₆₂-b-(PBO)₃₃ and two ionic surfactants, sodium dodecyl sulfate and hexadecyl trimethylammonium bromide, have also been investigated by fluorescence spectroscopy and DLS in detail.     

Preparation and characterization of stable monodisperse silver nanoparticles via photoreduction

Silver nanoparticles were synthesized by UV irradiation of [Ag(NH₃)₂]⁺ aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima around 420 nm. It was found that the formation rate of silver nanoparticles from Ag₂O was much quicker than that from AgNO₃, and the absorption intensity increased with PVP concentration as well as irradiation time. The maximum absorption wavelength (λ_max) was blue shift with increasing PVP content until 8 times concentration of [Ag(NH₃)₂]⁺ (wt%). The transmission electron microscopy (TEM) showed the resultant particles were 4–6 nm in size, monodisperse and uniform particle size distribution. X-ray diffraction (XRD) demonstrated that the colloidal nanoparticles were the pure silver. In addition, the silver nanoparticles prepared by the method were stable in aqueous solution over a period of 6 months at room temperature (25 °C).     

Synthesis of sodium-polystyrenesulfonate-grafted nanoparticles by core-cross-linking of block copolymer micelles

Sodium poly(styrenesulfonate)(polySSNa)-grafted polymer nanoparticles were synthesized by core-cross-linking of block copolymer micelles and subsequent chemical transformation. Block copolymers, poly(p-((1-methyl)silacyclobutyl)styrene-block-poly(neopentyl p-styrenesulfonate)s, polySBS-b-polySSPen, were synthesized by nitroxy-mediated living radical polymerization. The block copolymers formed micelles (R_h=15-23 nm, where R_h represents the hydrodynamic radius) with a polySBS core and polySSPen shell in acetone. The micelle core was cross-linked by ring-opening polymerization of silacyclobutyl groups in polySBS. Hydrolysis of the neopentyl groups provided polySSNa-grafted nanoparticles. The R_h of the particles before the hydrolysis ranged from 12 to 21 nm in acetone, while they varied to the range from 50 to 110 nm in water after the hydrolysis.     

Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis

Colloidal silver nanoparticles were synthesized by an easy green method using thermal treatment of aqueous solutions of silver nitrate and natural rubber latex (NRL) extracted from Hevea brasiliensis. The UV–Vis spectra detected the characteristic surface plasmonic absorption band around 435 nm. Both NRL and AgNO₃ contents in the reaction medium have influence in the Ag nanoparticles formation. Lower AgNO₃ concentration led to decreased particle size. The silver nanoparticles presented diameters ranging from 2 nm to 100 nm and had spherical shape. The selected area electron diffraction (SAED) patterns indicated that the silver nanoparticles have face centered cubic (fcc) crystalline structure. FTIR spectra suggest that reduction of the silver ions are facilitated by their interaction with the amine groups from ammonia, which is used for conservation of the NRL, whereas the stability of the particles results from cis-isoprene binding onto the surface of nanoparticles. Therefore natural rubber latex extracted from H. brasiliensis can be employed in the preparation of stable aqueous dispersions of silver nanoparticles acting as a dispersing and/or capping agent. Moreover, this work provides a new method for the synthesis of silver nanoparticles that is simple, easy to perform, pollutant free and inexpensive.     

Thermal behavior of carbon nanotubes decorated with gold nanoparticles

Three different forms of carbon, i.e., multi-walled carbon nanotubes (CNTs), single-walled CNTs, and soot, were decorated with gold nanoparticles by a new method. In this method C₁₀H₈ ⁻ ions transfer electrons to the CNTs or soot. These electrons on the carbon surface can then reduce Au³⁺ species to form supported Au nanoparticles with a narrow particle size distribution. Thermogravimetric/differential thermal analyses (TG/DTA), XRD, Raman, and TEM show that naphthalene molecules remain trapped inside the Au nanoparticles and can only be removed by treatment at ca. 300 °C. Remarkable effect of the Au nanoparticles on the oxidation of carbon by O₂ is also observed by TG/DTA, i.e., on-set oxidation temperature and activation energy (E _a). It is shown that as the Au particle size decreases from 25 to 2 nm a linear decrease of the oxidation temperature is observed. Au particles larger than 25 nm do not produce any significant effect on carbon oxidation. These results are discussed in terms of spillover catalytic effect where Au nanoparticles activate O₂ molecules to produce active oxygen species which oxidize the different carbon supports.     

Decorating multi-walled carbon nanotubes with nickel nanoparticles for selective hydrogenation of citral

The nanocomposites of multi-walled carbon nanotubes (MWNTs) decorated with nickel nanoparticles were conveniently prepared by a chemical reduction of nickel salt in the present of poly(acrylic acid) grafted MWNTs (PAA-g-MWNTs). Due to the strong interaction between Ni²⁺ and –COOH, PAA-g-MWNTs became an excellent supporting material for Ni nanoparticles. The morphology and distribution of Ni nanoparticles on the surface of MWNTs were greatly influenced by the reduction temperatures, the experimental results also showed that the distribution of Ni nanoparticles was greatly improved while the MWNTs were modified by poly(acrylic acid) (PAA). The hydrogenation activity and selectivity of MWNTs decorated with Ni nanoparticles (Ni-MWNTs) for α, β-unsaturated aldehyde (citral) were also studied, and the experimental results showed that the citronellal, an important raw material for flavoring and perfumery industries, is the favorable product with a percentage as high as 86.9%, which is 7 times higher than that of catalyst by Ni-supported active carbon (Ni-AC).     

Synthesis and properties of chitosan‐based thermo‐ and pH‐responsive nanoparticles and application in drug release

In this research, thermo‐ and pH‐responsive nanoparticles with an average diameter of about 50–200 nm were synthesized via the surfactant‐free emulsion polymerization. The thermal/pH dual responsive properties of these nanoparticles were designed by the addition of a pH sensitive monomer, acrylic acid (AA), to be copolymerized with N‐isopropylacrylamide (NIPAAm) in a chitosan (CS) solution. The molar ratio of CS/AA/NIPAAm in the feed was changed to investigate its effect on structure, morphology, thermal‐ and pH‐responsive properties of the nanoparticles. It was found that CS‐PAA‐PNIPAAm nanoparticles could be well dispersed in the aqueous solution and carried positive charges on the surface. The addition of thermal‐sensitive NIPAAm monomer affected the polymerization mechanism and interactions between CS and AA. The particle size of the nanoparticles was found to be varied with the composition of NIPAAm monomer in the feed. The synthesized nanoparticles exhibited stimuli‐responsive properties, and their mean diameter thus could be manipulated by changing pH value and temperature of the environment. The nanoparticles showed a continuous release of the encapsulated doxycycline hyclate up to 10 days during an in vitro release experiment. The environmentally responsive nanoparticles are expected to be used in many fields such as drug delivery system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2798–2810, 2009     

Semicontinuous microemulsion copolymerization of vinyl acetate and butyl acrylate: high solid content and effect of monomer addition rate

Vinyl acetate and butyl acrylate were copolymerized in microemulsion under monomer-starved conditions by a semicontinuous process using different monomer addition rates (R _a). A mixture of sodium dodecyl sulfate and polyethylene glycol dodecyl ether (Brij®35) were used as surfactants. Potassium persulfate was the initiator. High copolymer content latexes (around 40 wt.%), average particle diameters (D _p)?M _w) between 180,000 and 760,000. D _p and M _w of the copolymers decrease as R _a is decreased. As R _a increases, a shoulder in the molar mass distribution was observed at high values of M _w, which was ascribed to chain transfer to polymer. Homogeneous copolymer compositions were observed throughout the reaction, which cannot be obtained by the usual batch process.