Single page Theme & Template page

Hello everybody!

I have been going crazy dealing with a single page theme like this one.

I managed to have a loop of the pages in the index.php and link them through the WP menu. However when I try and give a different structure to the various sections issues arise.
The code that I used for this loop is the following:

<?php $args = array(
	'sort_order' => 'ASC',
	'sort_column' => 'menu_order', //post_title
	'hierarchical' => 1,
	'exclude' => '',
	'child_of' => 0,
	'parent' => -1,
	'exclude_tree' => '',
	'number' => '',
	'offset' => 0,
	'post_type' => 'page',
	'post_status' => 'publish'
);
$pages = get_pages($args);
//start loop
foreach ($pages as $page_data) {
    $content = apply_filters('the_content', $page_data->post_content);
    $title = $page_data->post_title;
    $slug = $page_data->post_name;
?>

<div id='<?php echo "$slug" ?>' class="section">
<div class="contentSlide">
<h2><?php echo "$title" ?></h2>
<?php echo "$content" ?>
</div>
</div>

<?php }; ?>

This shows all the pages one after the other.

What I want to do is assign a different structure depending on the template of the page (e.g. a different template for the gallery, one for the portfolio, one for the about page, …) with a code like that:

<?php if ( !is_page_template ('pagePortfolio.php')) { ?>
<div class="some_class_for_portfolio_page">SOME CONTENT</div>
<?php } else { ?>
<div class="some_class_for_not_portfolio_page">SOME DIFFERENT CONTENT</div>
<?php } ?>

….but that does not work at all ??
Anyone has an idea? Pleeeeeease <3<3<3