Asymmetrical Morphology and Performance of Composite Colloidal

Subscriber access provided by UNIV OF UTAH

Article

Asymmetrical morphology and performance of composite colloidal particles controlled via hydrophilic comonomer addition time in the presence of PVDF latex Yang Wang, Yongfang Yang, Jinfeng Yuan, Mingwang Pan, Gang Liu, Huili Ding, and Cuicui Ma Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 02 Jun 2017 Downloaded from http://pubs.acs.org on June 6, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Asymmetrical morphology and performance of composite

colloidal

particles

controlled

via

hydrophilic comonomer addition time in the presence of PVDF latex Yang Wang, Yongfang Yang, Jinfeng Yuan, Mingwang Pan*, Gang Liu, Huili Ding, Cuicui Ma Institute of Polymer Science and Engineering, Hebei University of Technology, Tianjin 300130, P. R. China

Keywords: seeded emulsion polymerization; hydrophilic-hydrophobicity; asymmetrical particle; morphology; confinement crystallization

ABSTRACT: Anisotropic composite latex particles with heteromorphous bowl-like and popcorn-like shape were fabricated by a general approach --- seeded emulsion polymerization. The

morphologies

of

acrylate-co-3-trimethoxysilyl

polyvinylidene propyl

fluoride@poly

methacrylate)

(styrene-co-butyl

composite

particles,

PVDF@P(St-co-BA-co-MPS), could be efficiently controlled by varying the feeding time of hydrophilic MPS. The deformation mechanism of bowl-like particles was largely attributed to

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

the diverse rigidities of P(St-co-BA-co-MPS) phase from the inhomogeneous crosslinking density formed through change the MPS feeding time. During the polymerization, the PVDF crystallization behaviors appeared an obvious transformation from unconfined to confined crystallization. Additionally, the chemical property and morphologies of the particles surface greatly impacted hydrophilic-hydrophobic character of the particles films. After capping the hydrophilic functional groups of the surface, the contact angle (165 o) of the bowl-like particles appeared much higher than that of the popcorn-like particles (112 o) due to more caves existing on the former surface, exhibiting a super-hydrophobicity.

Introduction Janus particles have triggered great attention owing to their multiple promising applications in photonic crystals1-3, biological sensors4-6, smart coatings7-9, drug carriers10,11, and self-assembly12-14. Among them, one of the major applications of the particles is to form super-hydrophobic coatings in which fluoropolymer is very popular alternative matrix resin like polyvinylidene fluoride (PVDF). Fluorine atom of PVDF can surround the carbon chain closely because of its small radius, which can form a “shielding cover” that makes the fluorine polymer have better durability and resistance to chemical corrosion.15 Meanwhile, the interface energy of the fluorine polymer is very low due to the low polarizability of C-F bond and high symmetry of its molecular structure, which allows PVDF to have satisfactory performances in hydrophobicity and oleophobicity. However, just as a result of the above characters of PVDF, it does not always combine with base material very well. By comparison, the PVDF Janus particles have amphipathic characteristics because of their anisotropic


Page 3 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


structure and chemical property, which makes the particles have a better combination with the substrate. Although we prepared snowman-like PVDF/PS composite particles by soap-free seeded emulsion polymerization based on surface nucleation mechanism16,17 and surface-initiated single electron transfer radical mechanism in our previous works 8,18, the relationships of the composition and morphology with the properties of the asymmetrical particles haven’t been specifically investigated. It is well known that the composition and structure of latex particles significantly affect the properties, which decide their corresponding applications. Therefore, it is primarily important to study the influence of morphology and constitution of latex particles. Up to now, a variety of Janus latex particles fabricated by means of multi-methods have been demonstrated,

such

as

snowman-shaped19-22,

popcorn-shaped23-25,

cone-shaped26,27,

raspberry-shaped28-34, bowl-shaped35,36, mushroom-shaped37 and so on. As far as we know, the syntheses of PVDF Janus particles with bowl-like and popcorn-like structure via seeded emulsion polymerization following surface nucleation mechanism have not been reported. At present, bowl-like38,39, erythrocyte-like40 or single-cavity41-43 particles are synthesized mainly through change the charging amount, the feeding method, or the addition times of the crosslinker divinylbenzene (DVB). In present study, the hydrophilic comonomer 3-(trimethoxysilyl) propyl methacrylate (MPS) was used to replace DVB for the preparation of PVDF Janus particles because MPS can be hydrolyzed in an aqueous system to obtain -OH groups on the surface of the particles. The formed -OH functional groups can be used conveniently in subsequent condensation crosslinking or further modification. As for the PVDF/PS Janus particles previously synthesized by PS domains nucleated



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 34

on the surface of PVDF seed particles, it is considered that PS polymer chains have a great rigidity, most probably causing poor adhesion to substrate materials in the future coating. Herein, butyl acrylate (BA) was introduced to improve the flexibility of the copolymer chain segments and the film-forming property of the particles. As a result, we synthesized well-defined crosslinked heteromorphous bowl-like and popcorn-like polyvinylidene fluoride@poly(styrene-co-butyl

acrylate-co-3-(trimethoxysilyl)

propyl

(PVDF@P(St-co-BA-co-MPS)) composite latex particles through

methacrylate

seeded emulsion

polymerization. And then the effects of the feeding times of MPS, the addition amount of BA comonomers and the reaction temperatures on the particle morphologies were investigated in this study. Furthermore, the relationship between morphologies and crystallization behaviors of the composite particles and the influence of the morphologies and constitutions of the particles surface on the hydrophilic-hydrophobicity of the particles film were also investigated. Because of the different hydrophilic-hydrophobic nature and the surface topography of the asymmetrical particles, the synthesized particles with asymmetrical morphology can be used in coating, colloidal surfactant, interfacial assembly and so on.

Materials and methods Materials and Treatment. The monomers, styrene (St, above 99.5%) and butyl acrylate (BA, above 99.5%) were purchased from Tianjin Chemical Reagent Research Institute Co., Ltd. and purified to remove the inhibitors through vacuum distillation under the elevated temperature. Purified St and BA monomers were stored in refrigerator (5 oC) before use. Poly(vinylidene fluoride) latex (PVDF, Kynar Latex 32) was kindly provided by Arkema


Page 5 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Inc. The PVDF latex was dialyzed for 14 days by a dialysis tube to remove free surfactant with a molecular weight cutoff of 7500 Da (Spectrum Laboratories, Inc.) prior to use. The aqueous solution in the dialysis beaker was changed with clean deionized water each day to get rid of free surfactant as much as possible. A latent crosslinking agent, 3-(trimethoxysilyl) propyl methacrylate (MPS, chemically pure, J&K Chemical Reagent Co., Ltd.) was not further purified. The initiator, potassium persulfate K2S2O8 (KPS, 99.5%, China Medicine Group Chemical Reagent Co., Ltd.) and dodecyltrichlorosilane (DTS, 97%, Tokyo Chemical Industry Co., Ltd.) were used without any further refinement. All of the water used was deionized. Synthesis

of

PVDF@P(St-co-BA-co-MPS)

composite

particles.

PVDF@P(St-co-BA -co-MPS) latex particles with controllable morphologies were synthesized by seeded emulsion polymerization through the surface nucleation mechanism using the treated PVDF particles as seeds. In detail, 2.50 g of PVDF emulsion (10 wt% solid content) and 14.75 g of deionized water were mixed in a 100 mL four-necked round-bottom flask with a mechanical stirrer, a condenser, a nitrogen inlet and a thermometer. In order to prevent any agglomeration of the latex particles, the system was ultrasonicated for 40 min. Then, the dispersion was purged with nitrogen gas to eliminate oxygen in the system and stirred with mechanical stirrer at a speed of 100 rpm. After 10 min, St (1.19 g) and BA (0.06 g) were added into the mixture, and swelling to seeds for 1 h at room temperature. Upon heating to 70 oC, the initiator KPS (0.01 g) was added into the above system to initiate the polymerization. Followed by the polymerization running at 70 oC for 1 h, the polymerization temperature was raised to 80 oC and the hydrophilic monomer MPS (0.03 g) was charged into



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 34

the reaction system. After polymerizing for 3 h, additional MPS (0.02 g) was recharged into the system and the reaction was terminated at 6 h of polymerization time. Characterization. Morphology of colloidal particles was observed by using scanning electron microscopy (SEM, Nano 450 at 10 kV, FEI, USA). In order to prepare SEM sample, several drops of PVDF@P(St-co-BA-co-MPS) colloid were diluted with deionized water to gain a translucent suspension, which was further ultrasonicated for 30 min. Then, one drop of the suspension was cast onto a conductive silicon wafer, and dried completely at room temperature. Then, the sample of the particles film was sputtered with Au by using a sputter coater (SC7620, Quorum, England) for 15 s to improve the quality of the images. Transmission electron microscopy (TEM) was used to characterize the internal structure of PVDF@P(St-co-BA-co-MPS) particles, which was carried out on an H-600 transmission electron microscope at 80 kV (Hitachi, Japan). The samples for TEM observation were prepared by spreading the above dilute colloid onto carbon-coated copper grids. Fourier Transform Infrared (FTIR) spectra were acquired on a Tensor-27 FTIR spectrometer (FTIR, Tensor-27, Bruck, Germany). Few powder samples mixing with desiccative potassium bromide (KBr) was pressed into sheets with a tabulating machine. The carbon, oxygen and silicon contents on the surfaces of the PVDF@P(St-co-BA-co-MPS) composite particles were confirmed by X-ray photoelectron spectroscopy (XPS, K-Aepna ThemoFisher, America). Crystallization behaviors of PVDF in the PVDF@P(St-co-BA-co-MPS) composites were investigated using a differential scanning calorimetry (DSC-800B, DuPont Company, USA) under a dry nitrogen atmosphere. About 3 mg of the composite sample was heated to 200 oC which is above the melting temperature of PVDF (∼175 oC) and a heating


Page 7 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


rate is 10 oC/min. Then the temperature held for 5 min to melt completely for eliminating heating history before cooling down to room temperature at a cooling rate of 10 oC/min. The particle sizes and size distributions of the colloidal particles in aqueous dispersions were analyzed by a Zeta-Sizer dynamic laser scattering particle size analyzer (DLS, 90 type, Malvern, England). The static water contact angle of the composite particle film was investigated by a DSA30S instrument (KRÜSS Co., Germany) at room temperature. To prepare polymer particle films, a certain amount of the corresponding emulsion was cast onto a glass slide and then dried at room temperature over 12 h before measurement.

Results and discussion Preparation of PVDF@P(St-co-BA-co-MPS) composite particles. Using the dialyzed PVDF as seeds, St, BA and MPS as comonomers, PVDF@P(St-co-BA-co-MPS) composite particles were fabricated by seeded emulsion polymerization. To understand the formation process of colloidal particles clearly, the morphology evolution and size growth of PVDF@P(St-co-BA-co-MPS) particles were investigated. SEM and TEM images of the PVDF seed particles and the PVDF@P(St-co-BA-co-MPS) latex particles at different reaction times are shown in Figure 1. As can be seen in Figure 1A, the PVDF seed particles show a regular spherical shape. After polymerizing for 1 h, the latex particle shows a clear snowman-like structure before charging MPS comonomer (Figure 1B). Based on our previous work16, the snowman-like particle was formed following a surface nucleation mechanism. After the MPS comonomer was charged into the system for 1 h, it is worthwhile to note that an obvious cavity appeared on the particles surface (Figure 1C), accompanied by



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 34

a rapid growth of the particles size from 253 nm to 312 nm, as shown in Figure 3Aa. After polymerization for 3 h, we recharged the MPS into the system and one deep large cavity and lots of small cavities on the particles surface can be observed (Figure 1D). With prolonging the polymerization time from 3 h to 6 h, there was little change occurring to the cavity-shape (Figure 1D to G) except a gradual increase of the latex size (338 nm-352 nm). And the heteromorphous bowl-like composite particles (HBPs) were fabricated at 6 h. Here, the TEM images of the bowl-like particles were also inserted in the SEM images of Figure 1 to show the internal structure. Because there was no VDF monomer incorporating in the polymerization system, the dark particles with a greater contrast inside the composite latex particles should be the PVDF seed particles.

Figure

1.

SEM

and

TEM

images

of

A)

PVDF

seed

particles

and

PVDF@P(St-co-BA-co-MPS) composite particles with heteromorphous bowl-like structure at different polymerization times of B) 1, C) 2, D) 3, E) 4, F) 5, G) 6 h, respectively. The scale bar in inserted TEM photos is 200 nm.


Page 9 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Influence of the feeding time of MPS comonomer on the particle morphologies. According to our previous work44, the hydrophilic comonomer MPS can be hydrolyzed during the polymerization and the MPS is important for the structure formation of the latex particles. And trialkoxysilane group in MPS can be hydrolyzed for coupling with each other while acrylate group in MPS can copolymerize with St and BA monomers. Therefore, we charged the MPS into the system together with St and BA comonomers during the swelling stage to study the effect of the addition time of hydrophilic comonomer MPS on the latex morphology. The SEM and TEM images of the PVDF@P(St-co-BA-co-MPS) latex particles prepared with early charging of MPS at different reaction times are shown in Figure 2. Firstly, the MPS charged together with St and BA comonomers were decentralized evenly on the surface of the PVDF seed particles at the swelling stage. Because St, BA, and MPS are highly immiscible with PVDF seeds, they cannot swell the PVDF seeds16. As a result, the PVDF@P(St-co-BA-co-MPS) composite particles in this system demonstrated a quite different morphology, comparing to the above case of the delayed addition MPS. After polymerization for 1 h, a number of tiny protrusions were nucleated on the surface of PVDF seeds, as shown in Figure 2A, and the protrusions were considered as P(St-co-BA-co-MPS) phase. The size had a little increment from 238 nm to 246 nm, as shown in Figure 3Ab. When the polymerization time was 2 h, the PVDF@P(St-co-BA-co-MPS) latex particles exhibited three or four large bulges and some irregular small bulges nucleated newly on the surface of PVDF particles (Figure 2B). As polymerizing for 3 h, it was clearly observed that the protrusions on the surface of PVDF seed particles became larger (Figure 2C) and the average size reached 258 nm (Figure 3Ab). At the same time, the number of the bulges exhibited on



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 34

the latex particles reduced due to the further merging of the P(St-co-BA-co-MPS) phase. With constant increase of the polymerization time, those irregular small bulges continued to grow and merge by absorbing near unreacting monomers to minimize the free energy.45 Upon further prolonging the polymerization time to 6 h, it is noticed that the number of bulges didn’t further reduce, as shown in Figure 2D to F. However, the size of particles still increased to 303 nm for the progressive growth of P(St-co-BA-co-MPS) phase. Finally, the PVDF seed particles were nearly entirely wrapped by the P(St-co-BA-co-MPS) protrusion phase and the popcorn-like composite particles (PCPs) were obtained.

Figure 2. SEM and TEM images of PVDF@P(St-co-BA-co-MPS) composite particles with popcorn-like shape at different polymerization times of A) 1, B) 2, C) 3, D) 4, E) 5, F) 6 h, respectively. The scale bar in inserted TEM photos is 200 nm.


Page 11 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure

3

shows

the

size

growth

and

size

distributions

of

the

PVDF@P(St-co-BA-co-MPS) composite particles with the above two morphologies (bowl-like and popcorn-like structure). The polydispersity index (PDI) of the composite particles was 0.108 for bowl-like structure (Figure 3Ba) while it was 0.069 for popcorn-like structure (Figure 3Bb). Figure 3A illustrates that the HBPs (from 238 nm to 351 nm) grew faster than the PCPs (from 238 nm to 303 nm) during polymerization and it caused the difference of the PDI value between the two morphologies. The delayed addition of MPS forming crosslinking caused a remarkable increase of the viscosity of reaction loci, thus leading to the increase of the growing rate of the particles. The DLS measurement generally assumes that the tested particles are symmetrically spherical. Whereas the HBPs appeared more irregular in shape compared with the PCPs, when the test laser light passed through the composite particles from different angles, the instrument would give different responses, also causing a bigger PDI value.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 34

Figure 3. A) Size growth of a) HBPs and b) PCPs at different reaction times (0-6 h); B) size distributions of a) HBPs and b) PCPs at 6 h of polymerization. The sizes and size distributions were obtained from DLS measurement.

Influence of the amount of BA comonomer. It is well known that PS macromolecular chain has a great rigidity and it doesn’t well combine with the substrate of the coating in the future application. Therefore, BA was added into the system to improve the flexibility of the copolymer chain segments. Herein, the impact of addition amount of BA monomer on the particles morphology was investigated, as shown in Figure 4. In these experiments, the MPS was added after polymerization for 1 h. When the addition amount of BA monomer was 0 wt%, the PVDF@P(St-co-MPS) colloid particles had a rougher surface 12 ACS Paragon Plus Environment

Page 13 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and the shrinkage degree of the P(St-co-MPS) shell was low (see Figure 4A). Without addition of BA monomer, the MPS could contact fully with the exclusive rigid PS phase, which made the composite particles surface become more rough and irregular due to both high incompatibility and different hydrophilic-hydrophobicity. As the feed mass ratio of BA monomer

was

5

wt%

based

on

the

St

monomer,

the

morphology

of

PVDF@P(St-co-BA-co-MPS) particles appeared several obvious depression and the shape of the particles became relative regular (Figure 4B). With further increasing the addition amount of BA monomer to 10 wt%, the surface of the composite particles became more smooth but there was a gap on it due to the existing hydrophilic MPS44,45, as shown in Figure 4C. When the amount of BA is high, more PBA constituents in the copolymer make the macromolecular chains become more flexible. The excessive flexibility leads to collapsing and further merging of the respective bulges on the particles, thus resulting in the relative smooth surface. It was concluded that adjusting the mass ratio between BA and St monomers could significantly change the morphology of the latex particles.

Figure 4. SEM images of PVDF@P(St-co-BA-co-MPS) composite particles with different amount of BA comonomer: A) 0 wt%, B) 5 wt%, and C) 10 wt% (all based on St monomer).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 34

Influence of polymerization temperature on the particles morphologies. Figure 5 shows the influence of initial reaction temperature on the morphology of the PVDF@P(St-co-BA-co-MPS) particles. In these experiments, the MPS was added after polymerization for 1 h. From Figure 5, it can be found that the composite particles appeared a dumpling shape with PVDF stuffing at 65 oC, and bowl-like shape at 70 oC. While the start reaction temperature reached 80

o

C, the as-prepared composite particles presented

inhomogeneous spherical shape, in which no obvious deformation was observed. That is to say, with the start reaction temperature raised, the deformability of composite particles decreased. This is mainly because that the polymerization rate of St and BA monomers was slower when the start reaction temperature was lower (65 oC). There were many unreacted St monomers left when the MPS was added into the system, so there were more chances to make the particles appear deformation. As the start reaction temperature rose to 80 oC, the reaction rate increased greatly. The PVDF seed was almost wrapped by the copolymer shell to form a core-shell structure while the MPS was fed into the reaction system, implying no significant deformation occurring for the composite particles. Therefore, the initial reaction temperature is important to control the morphology of the PVDF@ P(St-co-BA-co-MPS) particles.


Page 15 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. SEM images of morphologies of PVDF@P(St-co-BA-co-MPS) composite particles at different start reaction temperatures: A) 65 oC, B) 70 oC and C) 80 oC, respectively. The BA addition amount was 5 wt% based on St monomer. The polymerization time was 6h. The conversions of the St, BA and MPS comonomers in the reactions A, B and C were 80.5 %, 80.7% and 82.1 %, respectively.

Structure of the HBPs and PCPs. FTIR spectrum is used to confirm characteristic functional groups in the particles. The FTIR spectra of PVDF seed particles, PVDF@P(St-co-BA-co-MPS) composite particles with heteromorphous bowl-like and popcorn-like structure are shown in Figure 6. In the polymerization process, the HBPs and the PCPs had the same feed ratio. Therefore, both of them should show similar FTIR spectra, as shown in Figure 6B and C. The absorption peaks appeared at 2921 and 2845 cm-1 in the FTIR spectrum of PVDF seeds (Figure 6A) belong to the C-H stretching vibrations of PVDF. The absorption peaks at 880 cm-1, 1186 cm-1 and 1403 cm-1 were assigned to the C-C skeleton vibration, the C-F stretching vibration, and the C-H bending vibrations of PVDF, respectively.18 The sharp peak at 841 cm-1 can be assigned to vibration absorption from crystalline PVDF phases.17 The absorption peaks at 1403, 1186 and 880 cm-1 of PCPs are stronger than HBPs, which indicates that the content of PVDF in PCPs is higher than HBPs. The absorption peaks appearing at 699 and 756 cm-1 in the FTIR spectra of PVDF@P(St-co-BA-co-MPS) can be assigned to C-H bending vibration of benzene ring in PS, and the absorption peaks at 1450, 1491, and 1598 cm-1 can be attributed to the C=C skeletal vibrations of the benzene ring. The characteristic peak at 3026 cm-1 can be attributed



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 34

to the stretching vibrations of unsaturated C-H groups in benzene ring. It demonstrates that the St comonomer was copolymerized successfully. The characteristic peak at 1725cm-1 can be assigned to C=O stretching vibration from PBA. The band at around 3440 cm-1 may be assigned to the -OH which could come from the Si-OH group in the hydrolyzed MPS. Therefore,

the

above

results

indicates

that

the

bulge

phases

on

the

PVDF@P(St-co-BA-co-MPS) composite particles have the characteristics of PS and PBA.

Figure 6. FTIR spectra of A) PVDF seed particles, PVDF@P(St-co-BA-co-MPS) composite particles with B) heteromorphous bowl-like and C) popcorn-like structure.

To further confirm that the MPS was copolymerized at the surface of the composite particles, X-ray photoelectron spectroscopy (XPS) was utilized to investigate the surface composition of HBPs and PCPs. The corresponding XPS spectra are shown in Figure 7. A peak at 688 eV in the XPS spectrum of the PCPs (Figure 7B) was attributed to F 1s of PVDF, which was caused by the small isolated copolymer bulges distributing irregularly on the surface and incomplete covering of the PVDF core. However, no peak ascribed to F 1s was detected for the HBPs, since the PVDF core was wrapped with a thick copolymer shell and


Page 17 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the XPS test scope is only a few nanometers(

Asymmetrical Morphology and Performance of Composite Colloidal

Recommend Documents