# Textured and Hierarchically Constructed Polymer Micro- and Nanoparticles
## 3 Results  
### Textured Nanoparticles of Polymethylmethacrylate and Polydivinylbenzene  
In [11], wrinkled poly-DVB particles of about 2 um were synthesized in a two-step batch process; here, we tried to adopt microfluidics in order to achieve comparable results in a one-step semi-microfluidic process. We have experience in producing submicron PMMA particles with spherical [28], branched [33], and flower-like [34] shapes. The original idea about how the surface of such polymer particles becomes textured is as follows: As polymerization of DVB occurs, a three-dimensional network is gradually formed. The polymer particle gelates while there is still a considerable amount of monomer present. The rest of the monomer is removed in the following processing, resulting in shrinkage of the particle and wrinkling of its surface. This only works in a time interval when there is a certain ratio of cured polymer to the rest of the monomer. It does not work if the particle is too soft or already too stiff. Additionally, the addition of solvents such as toluene and ethanol promotes the formation of textured surfaces. We tried to simulate these effects first with the monomer MMA as follows:  
* The monomer phase consisted of 38% MMA, 62% toluene (volume fraction), and 11.6 mM AIBN. * The carrier phase consisted of 33% water, 67% methanol (volume fraction), and 1.0 mM SDS. Methanol was present because it was reported to improve the monodispersity of the resulting PMMA emulsions [35; 36]. * By means of the microfluidic hole-plate device (see Section 2.3[28]), an emulsion was produced at flow rates of 240 uL/min (monomer) and 1500 uL/min (carrier) and piped into a thermostat held at 85 \({}^{\circ}\)C.
* After a certain incubation time, EgDMA and DVB were added. The reason why these crosslinking components were not present from the start in the monomer phase was due to the assumption that when they are added later, they can accumulate near the particle surface, facilitating wrinkle formation. * With increasing reaction time, the mixture became increasingly turbid; after 4 h, it was removed from the thermostat. Coarse parts were removed manually; then, the suspension was centrifuged and washed several times, first with ethanol to extract remains of monomer and solvent and finally with water to remove the ethanol. In a series of experiments, the influences of the incubation time and the quantity of added EgDMA and DVB were investigated. Figure 1 depicts the influence of 1, 2, 3, and 5 min incubation time at a given crosslinker quantity of 680 ppm EgDMA + 6.8% DVB (volume fraction in relation to 100% monomer phase). After 5 min delay, the particle surface was rather sparsely textured. At 1 and 3 min delay, mainly irregular aggregates formed. The best results in terms of spherical, well-textured particles were obtained with a 2 min incubation time. With this parameter fixed, the influence of the crosslink composition was studied by omitting components of the initial two (Figure 2). Most textured surfaces were obtained with EgDMA alone or in combination with DVB. With DVB alone, the particles were more irregular, having the biggest substructures (knots). Without any crosslinker, particles looked similar to those upon late addition (Figure 1d). Table 1 summarizes the results of Figures 1 and 2. Figure 1: SEM images of PMMA particles. After distinct time intervals, 680 ppm EGDMA and 6.8% DVB (volume fractions) were added: (**a**) 1 min, (**b**) 2 min, (**c**) 3 min, and (**d**) 5 min. Figure 2: SEM images of PMMA particles. After 2 min, distinct crosslinker quantities (described as volume fraction relative to the monomer phase) were added: (**a**) 680 ppm EGDMA, (**b**) 6.8% DVB, (**c**) 680 ppm EGDMA + 6.8% DVB (as in Figure 1b), and (**d**) no crosslinker added. It can be seen that in the cases where distinct round particles were produced (Figures 1b,d and 2a,d), the particles had diameters of about 350-500 nm with surface substructures of 40-90 nm.