Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj Surface relief gratings in azopolyimides induced by pulsed laser irradiation Jolanta Konieczkowska a, ⁎ , Ewa Schab-Balcerzak a , Marcin Libera b , Ilarion Mihaila c , Ion Sava d, ⁎ a Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. Curie-Sklodowska Str., 41-819 Zabrze, Poland b Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland c “Alexandru Ioan Cuza” University of Iasi, Integrated Center of Environmental Science Studies in the North-Eastern Development Region (CERNESIM), Blvd. Carol I No. 11, Iasi 700506, Romania d “Petru Poni” Institute of Macromolecular Chemistry, Aleea Ghica Voda 41A, Iasi 700487, Romania ARTICLE INFO Keywords: Azobenzene Polyimides Surface relief gratings ABSTRACT The communication presents a study concerning the azo-polymer response to the pulse laser irradiation, in the context of the surface relief gratings (SRGs) inscription. We used the different energy density of the laser beam (10 and 45 mJ/cm 2 ) and their number of pulses (10 and 100) to observe the influence of the irradiation con- ditions on the amplitude of SRGs. The modulation of the polymer surface up to 440 nm was obtained. It was showed that key factors decided about polymer surface modulation depth, except irradiation conditions, are the azodye content in the polymer repeating units and flexibility of the polymer backbone. Moreover, unexpected effect of polymer molar masses on the SRG amplitudes was observed. The beneficial effect of higher polymer molar masses on SRGs formed using the stronger power of irradiation beam was found. 1. Introduction Photochromic polymers are materials containing a different photo- sensitive a structure such as spiropyranes, spirooxazines, stilbene or azobenzene molecules, which are able to change their optical properties under light irradiation [1]. Ones of the most interesting photochromic materials are azopolymers, containing azobenzene or azopyridine de- rivatives. Irradiation azopolymers with polarized light lead to re- versible trans-cis-trans isomerization of azobenzene moieties and may generate a perpendicular orientation of the azobenzene molecules to the electric vector of light [2]. The alignment gives rise. to the photo- induced optical. anisotropy (POA), that is photoinduced birefringence or dichroism appearing as an increased refractive index (Δn) or ab- sorption coefficient (α) [3]. The photoisomerization may also generate the sinusoidal deformation of film surface called surface relief gratings (SRGs), resulting from a macroscopic mass transport [3,4]. Formation SRGs by azopolymers induced their potential application eg. in the holographic recording of three-dimensional.objects with high resolu- tion [5], spectral filters in optical waveguides, and frequency-selective. mirrors in laser resonators [6,7], or as photomasks [8]. Due to the fact that azopolymers may be applied in large areas of photonics and op- toelectronics industries, the knowledge about their structure-property relationships, including the POA is necessary to further improve their optical response. Despite, many years of research structure-property relationships and mechanism of SRGs inscription in azopolymers are still unknown. To the best of our knowledge, in the literature, there is no information about the correlation between photoinduced bi- refringence, dichroism and the amplitude of SRGs, what has become the motivation for such research. Herein we present investigations concern SRGs formation in two kinds of azopolyimides (PIs), that is poly(amide imide)s (PAI) and poly (ester imide)s (PESI), which were comprehensively characterized in our previous works [9,10]. In these polymers azochromophores formed a side group and one aromatic ring of azobenzene is a part of the back- bone connected to the 2 and 4 positions with imide groups. They ex- hibited ones of the highest and the most stable values of the photo- induced birefringence, which have been described in the literature for azopolyimides. Their photoinduced birefringence was in the range 0.02–0.05 with stability in the dark 90–98.5%. Due to high and stable photoinduced birefringence, a large deformation of polymer surface in SRGs is expected. SRGs formation in others azopolyimides using a laser working in pulse mode was reported in previous works [11–16]. The aim of presented work was investigations of the relationship between azobenzene content in the polymer, its backbone structure, and molar masses together with values of the photoinduced bi- refringence and the amplitude of SRGs. It was believed that these complementary data would enable to get the better understanding of the respective structure–property relationships required for the devel- opment of high-performance polymers and also give some information about relations between the photoinduced birefringence and https://doi.org/10.1016/j.eurpolymj.2018.11.022 Received 21 June 2018; Received in revised form 10 October 2018; Accepted 13 November 2018 ⁎ Corresponding authors. E-mail addresses: jkonieczkowska@cmpw-pan.edu.pl (J. Konieczkowska), isava@icmpp.ro (I. Sava). European Polymer Journal 110 (2019) 85–89 Available online 14 November 2018 0014-3057/ © 2018 Elsevier Ltd. All rights reserved. T